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For genomic predictors to be of use in genetic evaluation, their predicted accuracy must be a reliable indicator of their utility, and thus unbiased. The objective of this paper was to evaluate the accuracy of prediction of genomic breeding values (GBV) using different clustering strategies and response variables. Red Angus genotypes (n = 9,763) were imputed to a reference 50K panel. The influence of clustering method [k-means, k-medoids, principal component (PC) analysis on the numerator relationship matrix (A) and the identical-by-state genomic relationship matrix (G) as both data and covariance matrices, and random] and response variables [deregressed estimated breeding values (DEBV) and adjusted phenotypes] were evaluated for cross-validation. The GBV were estimated using a Bayes C model for all traits. Traits for DEBV included birth weight (BWT), marbling (MARB), rib-eye area (REA), and yearling weight (YWT). Adjusted phenotypes included BWT, YWT, and ultrasonically measured intramuscular fat percentage and REA. Prediction accuracies were estimated using the genetic correlation between GBV and associated response variable using a bivariate animal model. A simulation mimicking a cattle population, replicated 5 times, was conducted to quantify differences between true and estimated accuracies. The simulation used the same clustering methods and response variables, with the addition of 2 genotyping strategies (random and top 25% of individuals), and forward validation. The prediction accuracies were estimated similarly, and true accuracies were estimated as the correlation between the residuals of a bivariate model including true breeding value (TBV) and GBV. Using the adjusted Rand index, random clusters were clearly different from relationship-based clustering methods. In both real and simulated data, random clustering consistently led to the largest estimates of accuracy, while no method was consistently associated with more or less bias than other methods. In simulation, random genotyping led to higher estimated accuracies than selection of the top 25% of individuals. Interestingly, random genotyping seemed to overpredict true accuracy while selective genotyping tended to underpredict accuracy. When forward in time validation was used, DEBV led to less biased estimates of GBV accuracy. Results suggest the highest, least biased GBV accuracies are associated with random genotyping and DEBV. [ABSTRACT FROM AUTHOR]

As input costs increase, producers need to be mindful of management practices to maintain profit margins and it is important to understand current management practices. Therefore, the objective of this study was to investigate current beef marketing strategies and beliefs of beef producers in the state of Mississippi in 2019. This survey was distributed to cattle producers in Mississippi in the June/July issue of "Cattle Business in Mississippi" magazine with return postage. There also was a link included in the "Monday Memo" email sent to members of the Mississippi Cattlemen's Association. The survey consisted of 22 questions that were divided into three sections: current practices, current cow-calf marketing practice, and general information. Responses from the survey were anonymous and confidential and were received via paper mail or electronic responses. Responses were stored and analyzed using Qualtrics. Data collected from this study were compared with 1999 data from a similar study conducted by Little et al. (2000). Out of 148 respondents, there was a 95% completion rate of surveys taken. Most respondents were 51 years and older with 54% of the respondents being part of the cattle industry for over 31 years. Ninety percent of respondents were members of the Mississippi Cattlemen's Association and almost 60% were certified in Beef Quality Assurance. The majority, 122 of 148 producers, stated their cattle operation was not the primary source of income for their household. The average number of cows, bulls, stockers/yearling, replacement heifers and cattle on-feed on an operation was greater in the 2019 data compared with 1999. On average, the number of cows per operation increased from 40 to 68 animals, bulls increased from 2 to 5 animals, and replacement heifers increased from 7 to 17 animals from 1999 to 2019. There was also an average increase from 30 to76 animals of stocker/yearling and an increase from 2 to 27 animals of on-feed cattle. Most producers vaccinate (81%) and deworm (85%) according to recommendations and indicated a lack of labor and time as reasons for not implementing some common management practices such as preconditioning. Respondents mainly purchased calves directly from a producer (61%) or from special sales (59%). In 1999, over one-half of respondents purchased from an auction. When it came to selling cattle, 58% of respondents sold at auction regularly in 2019. In 1999, 73% of respondents sold at auctions. In 2019, 72% of respondents stated they did not retain ownership while in 1999 only 58% of respondents did not retain ownership. In conclusion, our results suggest there have been key changes within the cattle industry regarding herd size increases and a shift in selling and purchasing habits since 1999. [ABSTRACT FROM AUTHOR]

Cattle health management in the feedlot sector continues to evolve and improve cattle welfare by promoting an understanding of illness and injury to minimize their effects. Many papers have focused on treating individual ill or injured cattle in cattle feeding facilities. However, care, treatment, and outcomes for chronically ill or injured cattle (“chronic cattle”) have received little attention in the literature. The purpose of this descriptive study was to present demographics, diagnoses, and outcomes of chronic cattle in 17 feedlots in the U.S. and Canada and discuss potential risk factors and welfare implications. Individual chronic cattle information and treatment records from 17 feedlots (U.S.: 8; Canada: 9) over 7 yr (2014 – 2020) were retrospectively retrieved from a large feedlot consulting and data-management service (Feedlot Health Management Services, a division of TELUS Agriculture Solutions Inc.). Chronic cattle were defined as those that had spent time in a feedlot’s designated chronic pen. Descriptive results are presented as means ± standard deviations. U.S. feedlots averaged 31,280 ± 23,231 cattle/yr, had an average chronicity rate of 2.24 ± 2.42 % (median 1.53%), and contributed 52,709 chronic cattle to the dataset. Canadian feedlots averaged 21,913 ± 10,497 cattle/yr, had an average chronicity rate of 1.41 ± 0.82% (median 1.10%), and contributed 15,940 chronic cattle to the dataset. U.S. chronic cattle were sourced across all seasons primarily from auctions and ranches, had an average arrival weight of 163 ± 59 kg, and an average days on feed (DOF) of 362 ± 172 d. Canadian chronic cattle were primarily auction-sourced in the fall, weighed 272 ± 95 kg at arrival, and averaged 246 ± 141 DOF. Chronic cattle were treated at least once for respiratory issues (U.S.: 46.3%; Canada: 26.9%), bullers (U.S.: 34.5%; Canada: 5.8%), musculoskeletal issues (U.S.: 2.2%; Canada: 1.4%), lameness (U.S.: 1.7%; Canada: 28.1%), metabolic issues (U.S.: 0.5%; Canada: 4.5%), or other diagnoses (U.S.: 2.2%; Canada: 6.3%), with many cattle treated for multiple issues (U.S.: 12.5%; Canada: 27.0%). Outcomes for chronic cattle were shipped (U.S.: 73.1%; Canada: 52.5%), railed (U.S.: 8.1%; Canada: 20.7%), euthanized (U.S.: 0.7%; Canada: 9.9%) died unassisted (U.S.: 18.1%; Canada: 16.2%), or transferred (U.S.: < 0.1%; Canada: 0.8%). These results are some of the first to describe chronic cattle populations and present interesting trends for further analysis. For example, differences in buller and lameness rates could reflect actual differences but may be artifices of the dataset and feedlot definitions. Additionally, high marketed cattle rates (shipped and railed) indicate positive outcomes for most cattle, but variable mortality rates merit further scrutiny [ABSTRACT FROM AUTHOR]

Macro- and microminerals are required for all physiological processes in beef cattle. When mineral deficiencies occur in pasture-based production systems, a multitude of deficiency symptoms may occur, and most often, these deficiencies result in hidden losses to include reduced production potential, reduced immunity, and reproductive failure. More severe deficiencies will result in specific deficiency symptoms, depending on the specific mineral deficiency. In pasture-based beef operations, specific deficiency symptoms are seldom observed. Forage mineral supply is highly variable and dependent on the forage type, stage of forage growth, and soil fertility. Grazing cattle mineral requirements change throughout the production cycle. With the variability of forage mineral supply and the changing mineral requirements, care must be taken when developing mineral supplementation programs for grazing cattle. The macrominerals function in nerve transmission, bone development, and metabolism and as electrolytes. These are Ca, P, Mg, Na, K, Cl, and S. The microminerals function in various areas of metabolism, immune responsiveness, reproductive efficiency, and many other functions. These minerals are Zn, Cu, Fe, I, Mn, Se, Mo, and Co. Of these macro- and microminerals, those that are important for supplementation to pasture-based cattle include Ca, P, Mg, Na, Cl, Zn, Cu, I, Mn, Se, and Co. However, the amounts to be supplemented will depend on the specific mineral requirements and the forage supply of the minerals. Consequently, the development of free-choice mineral supplementation programs is a moving target. Generally, this entangled mess is sorted by taking one mineral at a time into consideration. However, in doing so, one has to be cognizant of the many interactions that occur when changing intake of just 1 mineral in the supplement with respect to the amount supplied in the base forage. Often times, mineral nutrition problems of one or more minerals are created when trying to correct a deficiency of another mineral. This paper will address specific factors that are important to consider when developing and delivering mineral supplementation programs in pasture-based production systems in the Southeastern United States. [ABSTRACT FROM AUTHOR]

The objective of this paper was to estimate the genetic parameters of certain internal diseases (multifocal necrosis in the liver [MNL], bovine abdominal fat necrosis [BFN], and inflammation of the large intestine [ILI]) and to investigate relationships between the internal diseases and carcass traits (carcass weight [CW], rib eye area [REA], rib thickness [RT], subcutaneous fat thickness, and beef marbling score [BMS]). Records of the internal diseases and the carcass traits of 5,788 Japanese Black cattle were used for this study. The data for all the diseases were recorded as binary data as to whether the disease was observed (1) or not (0). Genetic parameters were estimated using linear and threshold animal models. The prevalence rates of MNL, BFN, and ILI were 16.1, 23.0, and 6.8%, respectively, and heritability estimates ± posterior SD were 0.18 ± 0.06, 0.28 ± 0.06, and 0.18 ± 0.06, respectively. The genetic correlations of MNL with BFN and ILI were -0.23 (P = 0.19) and -0.49 (P < 0.05), respectively. In contrast, the correlation between BFN and ILI was positive and high (0.96; P < 0.05). The phenotypic correlations of the internal diseases with the carcass traits were weak and not different from 0 except for those of BFN and ILI with CW, REA, and RT, which were all negative (P < 0.05) and ranged from -0.21 (ILI and CW) to -0.05 (BFN and RT). The genetic correlations of MNL with the carcass traits were all weak and not significant. In contrast, the genetic correlations of BFN and ILI with CW, REA, and RT were all negative and significant (P < 0.05) between BFN and CW (-0.36) and between BFN and RT (-0.33). However, the genetic correlations for BFN and ILI with BMS were all positive at 0.21 (P = 0.16) and 0.39 (P < 0.05), respectively. The estimated heritability of the internal diseases suggests that they can be genetically improved. Genetic relationships of BFN and ILI with meat quantity traits were favorable for beef cattle breeding, because lower disease liabilities were associated with improved CW, REA, and RT for BFN and ILI. However, rather strong and unfavorable genetic relationships were found between BFN or ILI and BMS, which is related to meat quality. This suggests that selection for animals with superior BMS would increasingly lead to animals with higher liability to the internal diseases. [ABSTRACT FROM AUTHOR]

This study evaluated 8 empirical models for their ability to accurately predict mean ruminal pH in beef cattle fed a wide range of diets. Models tested that use physically effective fiber (peNDF) as a dependent variable were Pitt et al. (1996, PIT), Mertens (1997, MER), Fox et al. (2004, FOX), Zebeli et al. (2006, ZB6), and Zebeli et al. (2008, ZB8), and those that use rumen VFA were Tamminga and Van Vuuren (1988, TAM), Lescoat and Sauvant (1995, LES), and Allen (1997, ALL). A data set of 65 published papers (231 treatment means) for beef cattle was assembled that included information on animal characteristics, diet composition, and ruminal fermentation and mean pH. Model evaluations were based on mean square prediction error (MSPE), concordance correlation coefficient (CCC), and regression analysis. The prediction potential of the models varied with low root MSPE (RMSPE) values of 4.94% and 5.37% for PIT and FOX, RMSPE values of 9.66% and 12.55% for ZB6 and MER, and intermediate RMSPE values of 5.66% to 6.26% for the other models. For PIT and FOX, with the lowest RMSPE, approximately 96% of MSPE was due to random error, whereas for ZB6 and MER, with the highest RMSPE, 15.85% and 23.42% of MSPE, respectively, was due to linear bias, and 37.19% and 60.12% of the error, respectively, was due to deviation of the regression slope from unity. The CCC was greatest for PIT (0.67) and FOX (0.62), followed by 0.60 for LES and TAM, 0.52 for ZB8, 0.39 for MER, 0.34 for ALL, and 0.22 for ZB6. Residuals plotted against model-predicted values showed linear bias (P < 0.001) for all models except PIT (P = 0.976) and FOX (P = 0.054) and mean bias (P < 0.001) except for FOX (P = 0.293), LES (P = 0.215), and TAM (P = 0.119). The study showed that the empirical models PIT and FOX, based on peNDF, and LES and TAM, based on VFA, are preferred over the others for prediction of mean ruminal pH in beef cattle fed a wide range of diets. Several animal (BW and intake), diet (forage and OM contents), and ruminal (ammonia and acetate concentrations) factors were (P < 0.001) related to the residuals for each model. We conclude that the accuracy of prediction of mean ruminal pH was relatively low for all extant models. Consideration of factors in addition to peNDF and total VFA, as well as the use of data from studies with continuous measurement of ruminal pH over 24 h or more, would be useful in the development of improved models for predicting ruminal pH in beef cattle. [ABSTRACT FROM AUTHOR]

The relationship between weather variables and dry matter intake (DMI) in beef steers was examined using daily intake data from 790 beef steers collected through a computer-controlled feeding system in nonsummer months. Daily data were condensed into weekly averages (N  = 13,895 steer-weeks). The variables considered to predict DMI (2.50 to 23.60 kg/d) were body weight (197 to 796 kg), dietary net energy for maintenance (NE m ; 0.79 to 2.97 Mcal/kg), ambient temperature (−23.73 °C to 21.40 °C), range of temperature (2.79 °C to 19.43 °C), dew point (−27.84 °C to 14.34 °C), wind speed (2.08 to 6.49 m/s), solar radiation (30.8 to 297.1 W/m2), and 2-wk lag (average of previous 2 wk's values) and monthly lag (average of previous 4 wk's values) of each weather variable. Toeplitz variance-covariance structure for repeated measures was used to determine the model to predict DMI, while accounting for the effects of body weight, dietary NEm, and other variables in the model. Two-week lag of ambient temperature interacted (P  ≤ 0.005) with 2-wk lag of range of temperature, monthly lag of wind speed, 2-wk lag of solar radiation, and dew point to predict DMI. Interactions (P  = 0.0001) between 2-wk lag of range of temperature vs. dew point and monthly lag of wind speed vs. 2-wk lag of solar radiation were also detected. This study reports important weather variables associated with differences in DMI of growing and finishing steers and will help improve the accuracy of DMI prediction equations for beef cattle. Improvements in the accuracy of predicting DMI should give producers better tools to plan and execute efficient feeding management programs. The R2 of the overall model was 0.8891. [ABSTRACT FROM AUTHOR]

This experiment evaluated the effects of roughage levels and supplemental fat on intake, growth performance, health, and physiological responses of newly received finishing cattle during 58-d receiving period. A total of 72 crossbred steers (initial body weight [BW] = 200 ± 13 kg) were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments, consisting of two roughage levels (wheat hay at 30% [R30] or 60% [R60]; dry matter [DM] basis) and two levels of supplemental fat (yellow grease at 0% [−FAT; no additional fat] or 3.5% [+FAT]; DM basis). Upon arrival, calves were individually weighed, blocked by off-truck shrunk BW, and assigned to 24 soil-surfaced pens (three calves per pen). Shrunk BW was also collected on day 58 for the calculation of average daily gain (ADG). Throughout the study, calves were assessed for bovine respiratory disease (BRD). Effects of roughage level × supplemental fat interaction were only observed for diet particle size distribution and estimated physically effective neutral detergent fiber (pe NDF) of diets (P ≤ 0.10). Adding fat to R60 diets tended to increase the percentage of particles retained in the 8-mm screen (P = 0.06) and the estimated pe NDF (P = 0.10), but did not affect R30 diets. Dietary roughage level did not affect DM intake (DMI; P = 0.85). Calves-fed R30 tended to have greater ADG and final BW than calves-fed R60 (P ≤ 0.08). Gain efficiency (gain:feed ratio; G:F) was greater for calves-fed R30 than calves-fed R60 (P = 0.01). Dietary roughage level did not affect morbidity and mortality (P ≥ 0.11). Supplemental fat did not affect DMI (P = 0.6) but tended (P = 0.09) to increase ADG compared to –FAT diets. The G:F was greater for calves-fed +FAT than –FAT (P = 0.03). The +FAT diet tended (P = 0.10) to increase the number of retreatments against BRD compared to −FAT, although the total number of antimicrobial treatments required to treat sick calves (P = 0.78) and the mortality rate (P = 0.99) were not affected by supplemental fat. Feeding +FAT diet tended (P ≤ 0.09) to increase plasma concentration of cortisol and immunoglobulin-G compared to –FAT. In summary, feeding 30% roughage diets or adding 3.5% yellow grease (DM basis) as supplemental fat increased G:F during the feedlot receiving period. [ABSTRACT FROM AUTHOR]

The objective was to determine the effects of injectable vitamin E (VE) before or after transit on feedlot cattle receiving performance, health, and blood parameters. Angus × Simmental steers (n = 196; body weight [ BW ] = 163 ± 29 kg) were utilized in a randomized complete block design. Steers were blocked by BW and randomly assigned to 1 of 3 treatments: intramuscular injections of saline pre- and post-transit (CON), intramuscular injections of VE (2,000 mg d-α-tocopherol) pre-transit and saline post-transit (PRE), or intramuscular injections of saline pre-transit and VE (2,000 mg d-α-tocopherol) post-transit (POST). Pre-transit injections were administered on day 0, and steers were transported on day 7 for approximately 4 h (348 km). After arrival, steers were fed a common corn silage-based diet in GrowSafe bunks. Final BW tended to be greater (P = 0.08) for CON steers compared with POST steers while PRE steers were intermediate. From days 7 to 63, treatment affected average daily gain (ADG) with PRE and CON steers exhibiting (P = 0.04) greater ADG compared with POST steers. Dry matter intake (DMI), water intake, and gain to feed from days 7 to 63 were not affected (P ≥ 0.17) by treatment. Day 0 serum α-tocopherol concentrations were considered marginal (2.3 ± 0.2 mg/l). A treatment × day interaction (P < 0.01) was observed for serum α-tocopherol concentrations. Serum α-tocopherol concentrations were greatest for PRE steers on day 7 (prior to and post-transit), but greater for POST steers on dys 10 and 14. Plasma ferric-reducing antioxidant potential concentrations increased (P = 0.04) for POST steers compared with CON steers and PRE steers being intermediate. Plasma non-esterified fatty acids (NEFA) concentrations exhibited a treatment × day interaction (P = 0.04) with CON and POST steers being 16% and 14% greater than PRE steers on day 14, respectively. On day 21, NEFA concentrations were greatest for POST steers compared with PRE steers and CON steers being intermediate. There was no main effect (P ≥ 0.14) of treatment on the number of bovine respiratory disease morbidity treatments. Hair cortisol concentrations were decreased (P < 0.01) 14 days after transit for PRE and POST steers compared with CON steers. Overall, injectable VE administered before or after transit increased serum tocopherol concentrations while reducing stress, but did not improve the growth performance of beef steers during the receiving phase. [ABSTRACT FROM AUTHOR]

Eighty-four Angus crossbred heifers (13 ± 1 mo of age, 329.5 ± 61.92 kg of body weight [BW]) were used in a generalized randomized block design with a 2 × 2 factorial arrangement of treatments. The factors evaluated were: 1) diet type (whole plant sorghum silage [ SS ] vs. byproducts-based [ BP ]), and 2) feed additive: Aspergillus oryzae prebiotic (AOP; 2 g/d) vs. Negative control (CTL; 0 g/d), resulting in four treatments: sorghum silage-control (SC), sorghum silage-AOP (SA), byproducts-control (BC), and byproducts-AOP (BA). Heifers were stratified by body weight (BW), randomly assigned to treatments (21 heifers per treatment) and housed in 12 pens equipped with two GrowSafe feed bunks each to measure individual dry matter intake (DMI). After a 14-d adaptation, BW was measured every 14 d for 56 d. Chewing activity was monitored through collar-mounted HR-Tags (heat-related tags). Following the performance period, apparent total tract digestibility was measured in 40 heifers, using indigestible neutral detergent fiber as a marker. Heifers fed with the BP diets had greater DMI (2.92% vs. 2.59% of BW, P < 0.01) and average daily gain (ADG ; 1.16 vs. 0.68 kg, P ≤ 0.01) than heifers fed with SS diets. Compared with BP-fed animals, heifers consuming the SS diets had 23 more visits/d to the feed bunks (P ≤ 0.01), consumed 53% less dry matter on each visit (P ≤ 0.01), and spent 39% more min chewing/d and 63% more min chewing/kg of DMI (P ≤ 0.01). However, chewing measured in min/kg of neutral detergent fiber intake was not affected by treatment (average 111.3 min/kg of NDF intake). Feeding AOP improved gain:feed (GF) by 15% in BP-fed heifers (0.120 vs. 0.104 kg/kg; P < 0.05). Inclusion of AOP increased organic matter digestibility (OMD) in SS diets (55.88% vs. 49.83%; P < 0.01), whereas it decreased OMD in BP diets (61.67% vs. 65.77%; P < 0.05). In conclusion, ADG and GF of BP-fed heifers was greater than SS-fed heifers, and GF was greater with AOP supplementation in BP-fed heifers. Improvement in GF in BP-fed heifers was likely not related to differences in nutrient digestibility as AOP inclusion did not enhance digestibility in the BP diet. Additionally, the effects of the AOP inclusion appear to be diet-dependent, where the 15% improvement in GF by AOP occurred in heifers fed with the more fermentable diet. Therefore, further research should explore the mechanisms responsible for the observed improvements in growth performance when feeding AOP to BP-fed heifers. [ABSTRACT FROM AUTHOR]

Rumen methanogenesis results in the loss of 6% to 10% of gross energy intake in cattle and globally is the single most significant source of anthropogenic methane (CH4) emissions. The purpose of this study was to analyze greenhouse gas traits recorded in a commercial feedlot unit to gain an understanding into the relationships between greenhouse gas traits and production traits. Methane and carbon dioxide (CO2) data recorded via multiple GreenFeed Emission Monitoring (GEM), systems as well as feed intake, live weight, ultrasound scanning data, and slaughter data were available on 1,099 animals destined for beef production, of which 648 were steers, 361 were heifers, and 90 were bulls. Phenotypic relationships between GEM emission measurements with feed intake, weight traits, muscle ultrasound data, and carcass traits were estimated. Utilization of GEM systems, daily patterns of methane output, and repeatability of GEM system measurements across averaging periods were also assessed. Methane concentrations varied with visit number, duration, and time of day of visit to the GEM system. Mean CH4 and CO2 varied between sex, with mean CH4 of 256.1 g/day ± 64.23 for steers, 234.7 g/day ± 59.46 for heifers, and 156.9 g/day ± 55.98 for young bulls. A 10-d average period of GEM system measurements were required for steers and heifers to achieve a minimum repeatability of 0.60; however, higher levels of repeatability were observed in animals that attended the GEM system more frequently. In contrast, CO2 emissions reached repeatability estimates >0.6 for steers and heifers in all averaging periods greater than 2-d, suggesting that cattle have a moderately consistent CO2 emission pattern across time periods. Animals with heavier bodyweights were observed to have higher levels of CH4 (correlation = 0.30) and CO2 production (correlation = 0.61), and when assessing direct methane, higher levels of dry matter intake were associated with higher methane output (correlation = 0.31). Results suggest that reducing CH4 can have a negative impact on growth and body composition of cattle. Methane ratio traits, such as methane yield and intensity were also evaluated, and while easy to understand and compare across populations, ratio traits are undesirable in animal breeding, due to the unpredictable level of response. Methane adjusted for dry matter intake and liveweight (Residual CH4) should be considered as an alternative emission trait when selecting for reduced emissions within breeding goals. [ABSTRACT FROM AUTHOR]

Forages are the base source of nutrition for any cow-calf operation. Forage types vary based on soil type and climate. Tall fescue (Lolium arundinaceum) is the most commonly used cultivated grass for grazing beef cattle in the United States. This cool-season perennial is easily established; is resistant to drought, insects, and nematodes; and has the ability to withstand heavy grazing pressure. Most tall fescue varieties are infected with the endophyte fungus (Neotyphodium coenophialum) that is essential for the plant's survival but detrimental to cattle performance. Ergot alkaloids are the generally accepted toxic agents produced by the fescue endophyte. Cattle that consume forages infected with this endophyte can develop fescue foot, fat necrosis, or fescue toxicosis. It is estimated that the beef industry loses over US$500 million annually due to fescue toxicosis through heat stress, reduced weight gain, suppressed appetite, and decreased reproductive performance. Other symptoms include a retained or rough hair coat and increased body temperature, which can be detrimental when animals are located in hot and or humid environments. Different forages and forage systems, feed additives, and animal management strategies have been tested through the years allowing the use of tall fescue in beef production systems while minimizing the adverse effects. An animal genetics approach needs to identify and select animals less susceptible to the ergot alkaloids. Research in this area reports that different cattle within the same herd can respond differently when grazing tall fescue, and evidence exists that breed type may also play a role in genetic tolerance to the negative effects on performance. Some studies have looked at the potential of identifying genetic markers that may assist in the selection of more resistant animals. From these studies, there is evidence that genetic variation does exist for resistance to the ergot alkaloids present when grazing endophyte-infected tall fescue. Forage management coupled with animal genetic selection could allow for more efficient use of tall fescue as a significant forage source in beef cattle systems. These would allow producing more beef per hectare in the United States in response to an increasing population combined with decreasing resources. [ABSTRACT FROM AUTHOR]

Manure N from cattle contributes to nitrate leaching, nitrous oxide, and ammonia emissions. Measurement of manure N outputs on commercial beef cattle operations is laborious, expensive, and impractical; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were to 1) collate an international dataset of N excretion in feces and urine based on individual observations from beef cattle; 2) determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; and 3) develop robust and reliable N excretion prediction models based on individual observation from beef cattle consuming various diets. A meta-analysis based on individual beef data from different experiments was carried out from a raw dataset including 1,004 observations from 33 experiments collected from 5 research institutes in Europe (n = 3), North America (n = 1), and South America (n = 1). A sequential approach was taken in developing models of increasing complexity by incrementally adding significant variables that affected fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models with experiment as a random effect. Simple models including dry matter intake (DMI) were better at predicting fecal N excretion than those using only dietary nutrient composition or body weight (BW). Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI. A model including DMI and dietary component concentrations led to the most robust prediction of fecal and urinary N excretion, generating root mean square prediction errors as a percentage of the observed mean values of 25.0% for feces and 25.6% for urine. Complex total manure N excretion models based on BW and dietary component concentrations led to the lowest prediction errors of about 14.6%. In conclusion, several models to predict N excretion already exist, but the ones developed in this study are based on individual observations encompassing larger variability than the previous developed models. In addition, models that include information on DMI or N intake are required for accurate prediction of fecal, urinary, and total manure N excretion. In the absence of intake data, equations have poor performance as compared with equations based on intake and dietary component concentrations. [ABSTRACT FROM AUTHOR]

The overarching aim was to examine the relationship of rectal temperature at fixed time artificial insemination (FTAI) on pregnancy outcomes in a typical breeding season with expected pregnancy rates approaching 50% using Bos indicus and Bos taurus cattle. This represents a continuum of steps to test the hypothesis that elevated body temperature at or around insemination is functionally important to maximize pregnancy outcomes. Rectal temperature of Bos indicus cattle at FTAI ranged from 37.0 to 40.9 °C; 60.6% were hyperthermic. Positive factors impacting pregnancy outcomes were rectal temperature at FTAI, body condition, and estrus patch scores. Rectal temperature at FTAI was positively associated with pregnancy outcomes (P < 0.0001); per each 1 °C increase pregnancy odds increased 1.9 times (95% CI: 1.4 to 2.6). Highest pregnancy outcomes occurred with rectal temperatures exceeding 40 °C (P = 0.0004). Rectal temperature before FTAI in Bos taurus cattle ranged from 37.8 to 41.8 °C; 43.3% were hyperthermic. Factors impacting pregnancy were rectal temperature at FTAI, estrus activity, parity, and ambient conditions on day of FTAI. Rectal temperature of Bos taurus cattle at FTAI was positively associated with pregnancy (P = 0.0286); odds increased 1.45 times (95% CI: 1.0 to 2.0) per each 1 °C increase. Highest pregnancy outcomes occurred with rectal temperatures at FTAI exceeding 40 °C (P = 0.057). Moreover, positive relationship of rectal temperature at FTAI to pregnancy persisted in estrual females (71.25% of total; P = 0.0408; OR 1.5; 95% CI: 1.0 to 2.2). Mindful that 1) elevated temperatures observed in Bos indicus and Bos taurus cattle directly promote meiotic resumption of the oocyte in vitro and that 2) in vivo hyperthermia alters intrafollicular components which others have shown to potentiate ovulation and promote meiotic resumption, it is biologically plausible that an acute elevation in body temperature at or around time of insemination is functionally important to maximize pregnancy outcomes. [ABSTRACT FROM AUTHOR]

The objective was to determine effects of old and new rubber matting in a slatted, indoor cattle feeding facility on cattle growth performance, locomotion, and carcass characteristics. In experiment 1, fall-born Angus × Simmental steers (N = 207; body weight = 222 ± 38 kg) were blocked by weight and assigned to 32 pens. Pens were randomly assigned to 1 of 4 treatments: no matting/concrete (CONC1), 12-yr-old Animat Pebble matting (OLD1), new Animat Maxgrip matting (MG), and new Animat Pebble matting (PEB1). Steers were fed a common diet for 209 d with a minimum stocking density of 3.40 m2 per animal. Final body weight (BW) and average daily gain (ADG) were affected (P = 0.02 and P < 0.01, respectively) by treatment with steers on PEB1 finishing heaviest with the greatest growth, MG and CONC1 intermediate, and OLD1 finishing at the lightest final BW with the least growth. Flooring treatment did not affect overall dry matter intake (DMI; P = 0.16) or gain to feed ratio (G:F; P = 0.94). Flooring treatment did not affect (P ≥ 0.19) any carcass traits. Locomotion scores (LS) were affected (P < 0.01) by flooring treatment with CONC1 having the worst mobility while OLD1, MG, and PEB1 were similar (P ≥ 0.24). Locomotion score had a day effect (P < 0.01) where cattle gait and mobility worsened as days on feed increased. In experiment 2, fall-born Angus × Simmental steers (N = 189; BW = 352 ± 43 kg) were blocked by weight and assigned to 21 pens. Pens were randomly assigned to 1 of 3 treatments: no matting/concrete (CONC2), 15-yr-old Animat Pebble matting (OLD2), and new Animat Pebble matting (PEB2). Steers were fed a common diet for 152 d with a stocking density of 2.65 m2 per steer. After 152 d on feed, flooring treatment did not affect (P ≥ 0.30) BW, ADG, or DMI nor did treatment affect (P ≥ 0.17) carcass traits. However, steers housed on OLD2 or PEB2 had improved locomotion scores (P = 0.02) compared with steers housed on CONC2. Locomotion score had a day effect (P < 0.01) as cattle gait and mobility worsened with greater number of days on feed, regardless of treatment. Overall, results suggest that new rubber matting increased ADG and HCW during a 209-d trial when cattle were stocked at 3.4 m2 in small pens and that rubber matting regardless of age improved cattle locomotion scores in slatted indoor feeding facilities. [ABSTRACT FROM AUTHOR]

Reliable predictions of metabolizable energy (ME) from digestible energy (DE) are necessary to prescribe nutrient requirements of beef cattle accurately. A previously developed database that included 87 treatment means from 23 respiration calorimetry studies has been updated to evaluate the efficiency of converting DE to ME by adding 47 treatment means from 11 additional studies. Diets were fed to growing-finishing cattle under individual feeding conditions. A citation-adjusted linear regression equation was developed where dietary ME concentration (Mcal/kg of dry matter [ DM ]) was the dependent variable and dietary DE concentration (Mcal/kg) was the independent variable: ME = 1.0001 × DE – 0.3926; r 2 = 0.99, root mean square prediction error [ RMSPE ] = 0.04, and P < 0.01 for the intercept and slope. The slope did not differ from unity (95% CI = 0.936 to 1.065); therefore, the intercept (95% CI = −0.567 to −0.218) defines the value of ME predicted from DE. For practical use, we recommend ME = DE – 0.39. Based on the relationship between DE and ME, we calculated the citation-adjusted loss of methane, which yielded a value of 0.2433 Mcal/kg of dry matter intake (DMI ; SE = 0.0134). This value was also adjusted for the effects of DMI above maintenance, yielding a citation-adjusted relationship: CH4, Mcal/kg = 0.3344 – 0.05639 × multiple of maintenance; r 2 = 0.536, RMSPE = 0.0245, and P < 0.01 for the intercept and slope. Both the 0.2433 value and the result of the intake-adjusted equation can be multiplied by DMI to yield an estimate of methane production. These two approaches were evaluated using a second, independent database comprising 129 data points from 29 published studies. Four equations in the literature that used DMI or intake energy to predict methane production also were evaluated with the second database. The mean bias was substantially greater for the two new equations, but slope bias was substantially less than noted for the other DMI-based equations. Our results suggest that ME for growing and finishing cattle can be predicted from DE across a wide range of diets, cattle types, and intake levels by simply subtracting a constant from DE. Mean bias associated with our two new methane emission equations suggests that further research is needed to determine whether coefficients to predict methane from DMI could be developed for specific diet types, levels of DMI relative to body weight, or other variables that affect the emission of methane. [ABSTRACT FROM AUTHOR]

Pulmonary hypertension is a noninfectious disease of cattle at altitudes > 1524 m (5,000 ft). Mean pulmonary arterial pressures (PAP) are used as an indicator for pulmonary hypertension in cattle. High PAP cattle (≥50 mmHg) entering the feedlot at moderate elevations have lower feed efficiency as compared to low PAP cattle (< 50 mmHg). The impact of pulmonary arterial pressure on mitochondrial function, oxidative phosphorylation (OXPHOS) protein abundance, and meat color was examined using longissimus lumborum (LL) from high (98 ± 13 mmHg; n = 5) and low (41 ± 3 mmHg; n = 6) PAP fattened Angus steers (live weight of 588 ± 38 kg) during early postmortem period (2 and 48 h) and retail display (days 1 to 9), respectively. High PAP muscle had greater (P = 0.013) OXPHOS-linked respiration and proton leak-associated respiration than low PAP muscles at 2 h postmortem but rapidly declined to be similar (P = 0.145) to low PAP muscle by 48 h postmortem. OXPHOS protein expression was higher (P = 0.045) in low PAP than high PAP muscle. During retail display, redness, chroma, hue, ratio of reflectance at 630 and 580 nm, and metmyoglobin reducing activity decreased faster (P < 0.05) in high PAP steaks than low PAP. Lipid oxidation significantly increased (P < 0.05) in high PAP steaks but not (P > 0.05) in low PAP. The results indicated that high PAP caused a lower OXPHOS efficiency and greater fuel oxidation rates under conditions of low ATP demand in premortem beef LL muscle; this could explain the lower feed efficiency in high PAP feedlot cattle compared to low PAP counterparts. Mitochondrial integral function (membrane integrity or/and protein function) declined faster in high PAP than low PAP muscle at early postmortem. LL steaks from high PAP animals had lower color stability than those from the low PAP animals during simulated retail display, which could be partially attributed to the loss of muscle mitochondrial function at early postmortem by ROS damage in high PAP muscle. [ABSTRACT FROM AUTHOR]

To quantify the effects of the TDN and CP in the diet of pregnant beef cows on fetal weight and birth weight of calves, a systematic review and meta-analysis were performed. We searched on 2 electronic databases (Scopus and ISI Web of Knowledge) from 1945 to October 2016, and we checked references of relevant review papers. Data were extracted using predefined protocols. Inclusion criteria were complete studies using pregnant beef cows receiving different diets that analyzed fetal weight and/or birth weight of calves. Random effect meta-analyses were conducted for each indicator separately with the mean of the control and the treated group. The analysis was conducted with the TDN and CP levels in relation to cows' requirements (NRC, 1996). The results were presented with the pooled mean difference (MD) and I² (the percentage of total variation between studies that is due to heterogeneity rather than chance). For fetal weight at 4 mo (FW4), we included 4 studies reporting 6 trials involving 170 animals; for fetal weight at 8 mo (FW8), we included 4 studies, 4 trials, and 156 animals; and for birth weight of calves (BiW), we included 48 studies, 125 trials, and 9,053 animals. The heterogeneity between studies was high for FW4 (I² = 94.4%), FW8 (I² = 91.08%), and BiW (I² = 96.9%). When control cows received 20 to 40% less TDN than the treated group, the FW4 was reduced by 2.27 kg (P < 0.001; I² = 65.06), because both groups received 19 to 25% more TDN than their requirements. The cows from control group tended to show (P = 0.057) a lower MD (1.57 kg; I² = 91.08%) when consuming 30% of CP above their requirements. The fetuses from control group were 2.23 kg lighter (P < 0.001; I² = 0%) when their cows consumed 20% TDN above their requirements. The BiW was lower (MD = -0.761; I² = 96.4%; P < 0.001) only for cows in the third period of pregnancy. The calves from both groups were born 0.560 and 0.761 kg lighter when cows consumed CP (P = 0.0015; I² = 97.1%) and TDN (P < 0.001; I² = 96.4%) more than their requirements, respectively. Our study demonstrates that FW4, FW8, and BiW were reduced when CP was 19 to 25% and TDN was 30% above of cows' requirements as published by the NRC (1996). [ABSTRACT FROM AUTHOR]

A diversity of forages with different types and concentrations of nutrients and plant secondary compounds may lead to complementary relationships that enhance cattle performance and welfare. We determined whether grazing combinations of tanniferous legumes (Lotus corniculatus , birdsfoot trefoil [BFT], Onobrychis viciifolia , sainfoin [SF]), and alfalfa [ALF] (Medicago sativa) influence foraging behavior, performance, and hair cortisol concentration in beef cattle compared with grazing the same legumes as monocultures. Twenty-one pairs of heifers grazed three spatial replications of seven treatments: monocultures of BFT, SF, or ALF, and all possible two- and three-way choices among strips of these legumes: SF-BFT, ALF-BFT, ALF-SF, and ALF-SF-BFT in two periods of 25 d each (adaptation phase + experimental period) during two consecutive years. The lowest incidence of grazing events occurred in the BFT treatment (42.0% of the total scans recorded; P < 0.10), with the rest of the treatments ranging between 47.8% (SF-BFT) and 52.6% (ALF-SF) of the total scans recorded. Heifers selected a varied diet, preferring SF over BFT or ALF in a 46:27:27 ratio for the three-way choice, and in a 70:30 ratio for both two-way choices. Heifers preferred BFT over ALF (62:38 ratio) in a two-way choice. All treatments followed similar daily grazing patterns (P > 0.10), with two major grazing events (1 h after sunrise and 3 h before dark). No differences among treatments were observed for the number of steps taken by heifers on a daily basis, motion index, or the percentage of time heifers spent standing (1,599, 5,356, and 45.3%, respectively; P > 0.10), suggesting that heifers on choice treatments did not invest extra time in walking, searching, or patch switching activities relative to heifers grazing monocultures. Heifers grazing the three-way choice gained more body weight (1.27 kg/d) than the average gains observed for animals grazing in all legume monocultures (1.00 kg/d; P = 0.014) or two-way choices (0.97 kg/d; P = 0.007), suggesting a synergism among pasture species for the treatment with the highest diversity. No differences in hair cortisol concentration were observed among treatments, with values ranging between 1.4 (BFT) and 2.12 ng/g (three-way choice; P > 0.10). Thus, forage diversity has the potential to enhance animal performance without affecting grazing efficiency, likely explained by the spatial arrangement of the forage species presented in the study. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of water quality on water intake (WI), forage intake, diet digestibility, and blood constituents in beef cows and growing beef heifers. This was a replicated 5 × 5 Latin square with five drinking water treatments within each square: 1) fresh water (Control); 2) brackish water (100 BRW treatment) with approximately 6,000 mg/kg total dissolved solids (TDS); 3) same TDS level as 100 BRW achieved by addition of NaCl to fresh water (100 SLW); 4) 50% brackish water and 50% fresh water to achieve approximately 3,000 mg/kg TDS (50 BRW); and 5) same TDS level as 50 BRW achieved by addition of NaCl to fresh water (50 SLW). Each of the five 21-d periods consisted of 14 d of adaptation and 5 d of data collection. Animals were housed individually and fed mixed alfalfa (Medicago sativa) grass hay cubes. Feed and WI were recorded daily. Data were analyzed with animal as the experimental unit. Age, treatment, and age × treatment were fixed effects, and animal ID within age was the random variable for intake, digestibility, and blood parameter data. Water and feed intake were greater than expected, regardless of age or water treatment. No treatment × age interactions were identified for WI (P = 0.71), WI expressed as g/kg body weight (BW; P = 0.70), or dry matter intake (DMI; P = 0.21). However, there was an age × treatment tendency for DMI when scaled to BW (P = 0.09) in cows consuming 100 BRW compared with fresh water. No differences were found for the other three treatments. Heifers provided 50 SLW water consumed less (P < 0.05) feed (g/kg BW) compared with heifers provided fresh water and 100 BRW. No differences (P > 0.05) in water, DMI, feed intake, or diet digestibility were found due to water quality treatment. In conclusion, under these conditions, neither absolute WI, absolute DMI, nor diet digestibility was influenced by the natural brackish or saline water used in this experiment. These results suggest that further research is necessary to determine thresholds for TDS or salinity concentration resulting in reduced water and/or feed intake and diet digestibility. [ABSTRACT FROM AUTHOR]

Understanding the utilization of feed energy is essential for precision feeding in beef cattle production. We aimed to assess whether predicting the metabolizable energy (ME) to digestible energy (DE) ratio (MDR), rather than a prediction of ME with DE, is feasible and to develop a model equation to predict MDR in beef cattle. We constructed a literature database based on published data. A meta-analysis was conducted with 306 means from 69 studies containing both dietary DE and ME concentrations measured by calorimetry to test whether exclusion of the y -intercept is adequate in the linear relationship between DE and ME. A random coefficient model with study as the random variable was used to develop equations to predict MDR in growing and finishing beef cattle. Routinely measured or calculated variables in the field (body weight, age, daily gain, intake, and dietary nutrient components) were chosen as explanatory variables. The developed equations were evaluated with other published equations. The no-intercept linear equation was found to represent the relationship between DE and ME more appropriately than the equation with a y -intercept. The y -intercept (−0.025 ± 0.0525) was not different from 0 (P = 0.638), and Akaike and Bayesian information criteria of the no-intercept model were smaller than those with the y -intercept. Within our growing and finishing cattle data, the animal's physiological stage was not a significant variable affecting MDR after accounting for the study effect (P = 0.213). The mean (±SE) of MDR was 0.849 (±0.0063). The best equation for predicting MDR (n = 106 from 28 studies) was 0.9410 (± 0.02160) +0.0042 (± 0.00186) × DMI (kg) – 0.0017 (± 0.00024) × NDF(% DM) – 0.0022 (± 0.00084) × CP(% DM). We also presented a model with a positive coefficient for the ether extract (n = 80 from 22 studies). When using these equations, the observed ME was predicted with high precision (R 2 = 0.92). The model accuracy was also high, as shown by the high concordance correlation coefficient (>0.95) and small root mean square error of prediction (RMSEP), <5% of the observed mean. Moreover, a significant portion of the RMSEP was due to random bias (> 93%), without mean or slope bias (P > 0.05). We concluded that dietary ME in beef cattle could be accurately estimated from dietary DE and its conversion factor, MDR, predicted by the dry matter intake and concentration of several dietary nutrients, using the 2 equations developed in this study. [ABSTRACT FROM AUTHOR]

With a growing global population and increased environmental concerns around animal agriculture, it is essential to humanely maximize animal performance and reduce environmental emissions. This study aims to determine the efficacy of feeding ractopamine hydrochloride (RAC), an orally active, β 1-adrenergic agonist (β1AA), to feedlot steers in the last 42 d of finishing to reduce ammonia (NH3) emissions and improve animal performance. A randomized complete block design was used to allocate 112 Angus and crossbred Angus steers (initial body weight [BW] = 566.0 ± 10.4 kg) to 8 cattle pen enclosures. Pens (n = 4 per treatment, 14 steers per pen, and 56 steers per treatment) were randomly assigned to one of two treatments: 1) CON; finishing ration containing no RAC, 2) RAC; finishing ration containing 27.3 g/907 kg dry matter (DM) basis RAC. Steers were weighed on day −1 and 0 before treatment and day 14, 28, and 42 during treatment. Treatment rations were mixed and delivered daily by masked personnel. Measured emissions included NH3, nitrous oxide (N2O), methane (CH4), hydrogen sulfide (H2S), and carbon dioxide (CO2). The primary response variables assessed were emissions standardized by live weight (LW) and hot carcass weight (HCW). Steers were harvested on day 43 and carcass data were collected on day 43 and 44. Steers fed RAC reduced NH3 emissions by 17.21% from day 0 to 28 (P = 0.032) and tended to reduce NH3 from day 0 to 42 by 11.07% (P = 0.070) vs. CON. When standardized for LW, NH3 was reduced by 23.88% from day 0 to 14 (P = 0.018), 17.80% from day 0 to 28 (P = 0.006), and 12.50% for day 0 to 42 (P = 0.027) in steers fed RAC vs. CON. Steers fed RAC had 14.05% (P = 0.013) lower cumulative NH3 emissions when standardized by HCW vs. CON. Feeding RAC to Steers reduced H2S by 29.49% from day 0 to 14 (P = 0.009) and tended to reduce H2S over day 0 to 28 by 11.14% (P = 0.086) vs. CON. When H2S emissions were standardized for LW, RAC fed steers had a 28.81% reduction from day 0 to 14 (P = 0.008) vs. CON. From day 0 to 42 the RAC fed steers tended to have a 0.24 kg/d greater average daily gain (ADG) (P = 0.066) and tended to eat 4.27% less (P = 0.069) on a DM basis vs. CON. The RAC fed steers had a 19.95% greater gain to feed ratio (G:F) compared to CON (P = 0.012). Steers fed RAC had an average of 12.52 kg greater HCW (P = 0.006) and an increase of 1.93 percentage units in dressing percent (DP) (P = 0.004) vs. CON. Ractopamine is an effective medicated feed additive for reducing NH3 and improving end product performance through HCW yields. [ABSTRACT FROM AUTHOR]

The addition of natural plant secondary compounds to ruminant feed has been extensively studied because of their ability to modify digestive and metabolic functions, resulting in a potential reduction in greenhouse gas emissions, among other benefits. Condensed tannin (CT) supplementation may alter ruminal fermentation and mitigate methane (CH4 ) emissions. This study’s objective was to determine the effect of quebracho CT extract [QT; Schinopsis quebracho-colorado (Schltdl.) F.A. Barkley & T. Meyer] within a roughage-based diet on ruminal digestibility and kinetic parameters by using the in situ and in vitro gas production techniques, in addition to blood urea nitrogen (BUN) and ruminal (volatile fatty acid [VFA], NH3 -N, and protozoa count) parameters. Twenty rumen-cannulated steers were randomly assigned to four dietary treatments: QT at 0%, 1%, 2%, and 3% of dry matter (DM; QT0: 0% CT, QT1: 0.70% CT, QT2: 1.41% CT, and QT3: 2.13% CT). The in situ DM digestibility increased linearly (P = 0.048) as QT inclusion increased, whereas in situ neutral detergent fiber digestibility (NDFD) was not altered among treatments (P = 0.980). Neither total VFA concentration nor acetate-to-propionate ratio differed among dietary treatments (P = 0.470 and P = 0.873, respectively). However, QT3 had lower isovalerate and isobutyrate concentrations compared with QT0 (P ≤ 0.025). Ruminal NH3 and BUN tended to decline (P ≤ 0.075) in a linear fashion as QT inclusion increased, suggesting decreased deamination of feed protein. Ruminal protozoa count was reduced in quadratic fashion (P = 0.005) as QT inclusion increased, where QT1 and QT2 were lower compared with QT0 and QT3. Urinary N excretion tended to reduce in a linear fashion (P = 0.080) as QT increased. There was a treatment (TRT) × Day interaction for in vitro total gas production and fractional rate of gas production (P = 0.013 and P = 0.007, respectively), and in vitro NDFD tended to be greater for QT treatments compared with no QT inclusion (P = 0.077). There was a TRT × Day interaction (P = 0.001) on CH4 production, with QT3 having less CH4 production relative to QT0 on day 0 and QT2 on days 7 and 28. Feeding QT up to 3% of the dietary DM in a roughage-based diet did not sacrifice the overall DM digestibility and ruminal parameters over time. Still, it is unclear why QT2 did not follow the same pattern as in vitro gas parameters. Detailed evaluations of amino acid degradation might be required to fully define CT influences on ruminal fermentation parameters and CH4 production. [ABSTRACT FROM AUTHOR]

The stability of genomic evaluations depends on the amount of data and population parameters. When the dataset is large enough to estimate the value of nearly all independent chromosome segments (~10K in American Angus cattle), the accuracy and persistency of breeding values will be high. The objective of this study was to investigate changes in estimated breeding values (EBV) and genomic EBV (GEBV) across monthly evaluations for 1 yr in a large genotyped population of beef cattle. The American Angus data used included 8.2 million records for birth weight, 8.9 for weaning weight, and 4.4 for postweaning gain. A total of 10.1 million animals born until December 2017 had pedigree information, and 484,074 were genotyped. A truncated dataset included animals born until December 2016. To mimic a scenario with monthly evaluations, 2017 data were added 1 mo at a time to estimate EBV using best linear unbiased prediction (BLUP) and GEBV using single-step genomic BLUP with the algorithm for proven and young (APY) with core group fixed for 1 yr or updated monthly. Predictions from monthly evaluations in 2017 were contrasted with the predictions of the evaluation in December 2016 or the previous month for all genotyped animals born until December 2016 with or without their own phenotypes or progeny phenotypes. Changes in EBV and GEBV were similar across traits, and only results for weaning weight are presented. Correlations between evaluations from December 2016 and the 12 consecutive evaluations were ≥0.97 for EBV and ≥0.99 for GEBV. Average absolute changes for EBV were about two times smaller than for GEBV, except for animals with new progeny phenotypes (≤0.12 and ≤0.11 additive genetic SD [ SDa ] for EBV and GEBV). The maximum absolute changes for EBV (≤2.95 SDa) were greater than for GEBV (≤1.59 SDa). The average(maximum) absolute GEBV changes for young animals from December 2016 to January and December 2017 ranged from 0.05(0.25) to 0.10(0.53) SDa. Corresponding ranges for animals with new progeny phenotypes were from 0.05(0.88) to 0.11(1.59) SDa for GEBV changes. The average absolute change in EBV(GEBV) from December 2016 to December 2017 for sires with ≤50 progeny phenotypes was 0.26(0.14) and for sires with >50 progeny phenotypes was 0.25(0.16) SDa. Updating the core group in APY without adding data created an average absolute change of 0.07 SDa in GEBV. Genomic evaluations in large genotyped populations are as stable and persistent as the traditional genetic evaluations, with less extreme changes. [ABSTRACT FROM AUTHOR]

Shade is a mechanism to reduce heat load providing cattle with an environment supportive of their welfare needs. Although heat stress has been extensively reviewed, researched, and addressed in dairy production systems, it has not been investigated in the same manner in the beef cattle supply chain. Like all animals, beef cattle are susceptible to heat stress if they are unable to dissipate heat during times of elevated ambient temperatures. There are many factors that impact heat stress susceptibility in beef cattle throughout the different supply chain sectors, many of which relate to the production system, that is, availability of shade, microclimate of environment, and nutrition management. The results from studies evaluating the effects of shade on production and welfare are difficult to compare due to variation in structural design, construction materials used, height, shape, and area of shade provided. Additionally, depending on operation location, shade may or may not be beneficial during all times of the year, which can influence the decision to make shade a permanent part of management systems. Shade has been shown to lessen the physiologic response of cattle to heat stress. Shaded cattle exhibit lower respiration rates, body temperatures, and panting scores compared with unshaded cattle in weather that increases the risk of heat stress. Results from studies investigating the provision of shade indicate that cattle seek shade in hot weather. The impact of shade on behavioral patterns is inconsistent in the current body of research, with some studies indicating that shade provision impacts behavior and other studies reporting no difference between shaded and unshaded groups. Analysis of performance and carcass characteristics across feedlot studies demonstrated that shaded cattle had increased ADG, improved feed efficiency, HCW, and dressing percentage when compared with cattle without shade. Despite the documented benefits of shade, current industry statistics, although severely limited in scope, indicate low shade implementation rates in feedlots and data in other supply chain sectors do not exist. Industry guidelines and third-party on-farm certification programs articulate the critical need for protection from extreme weather but are not consistent in providing specific recommendations and requirements. Future efforts should include: updated economic analyses of cost vs. benefit of shade implementation, exploration of producer perspectives and needs relative to shade, consideration of shade impacts in the cow–calf and slaughter plant segments of the supply chain, and integration of indicators of affective (mental) state and preference in research studies to enhance the holistic assessment of cattle welfare. [ABSTRACT FROM AUTHOR]

To address the gaps in current scientific knowledge, the objective of the present study was to investigate the impact of fumonisin exposure on feedlot cattle intake and performance. Fifty steers were received (day 0; 361 ± 6.4 kg), housed individually and fed once daily at 0800 hours. All steers were transitioned to a dry-rolled corn-based finishing diet from days 0 to 21 and then were fed the control finishing diet until day 50. Treatment diets were formulated to achieve ≤5 (CON), 15 (15PPM), 30 (30PPM), 60 (60PPM), or 90 ppm (90PPM) of total dietary fumonisin. Steers were fed the fumonisin treatment diets from day 50 until harvest on day 160; individual animal body weights (BW) were measured on days 0, 50, 100, 150, 159, and 160. Liver, kidney, and skeletal muscle tissue samples were collected at harvest for histopathological analyses, and liver samples were further analyzed for sphinganine (SA) and sphingosine (SO) concentration. Animal performance, carcass data, and liver enzyme concentration were analyzed using a mixed model; categorical data were analyzed via nonparametric models. Contrasts were used to test for linear and quadratic responses. Throughout the study, there was no effect of treatment (P > 0.60), or a linear response (P > 0.16) from increasing fumonisin levels, on BW or dry matter intake (DMI). However, CON tended to have a lower average daily gain (ADG) than the fumonisin treatments during the fumonisin treatment period (P = 0.10), and there was a positive linear response (P = 0.02) of ADG to fumonisin during the treatment period. There were no treatment differences in hot carcass weight, dressing percentage, marbling score, ribeye area, or yield grade. There were no effects of treatment on either liver abscesses (P = 0.95) or telangiectasis (P = 0.13). We observed a treatment difference for SA and SA:SO (P < 0.01), as well as a quadratic response (P < 0.02); both SA and SA:SO increased as dietary fumonisin increased. There were no observed differences between treatments for histopathology scores of kidney (P = 0.16), liver (P = 0.25), or skeletal muscle (P = 0.59) tissue. No adverse effects were observed in steers fed increasing dietary levels of fumonisin for 110 d prior to harvest. While elevated liver amino alcohol concentration did occur, negative effects on growth and carcass characters were not observed. [ABSTRACT FROM AUTHOR]

This experiment evaluated the impacts of administering a bovine appeasing substance (BAS) at feedlot entry to receiving cattle. Angus-influenced steers (n = 342) from 16 sources were purchased from an auction yard on day –1, and transported (12 hr; 4 trucks) to the feedlot. Upon arrival on day 0, shrunk body weight (BW; 240 ± 1 kg) was recorded and steers were ranked by load, shrunk BW, and source and assigned to receive BAS (IRSEA Group, Quartier Salignan, France; n = 171) or placebo (diethylene glycol monoethyl ether; CON; n = 171). The BAS is a mixture of fatty acids that replicate the composition of the bovine appeasing pheromone. Treatments (5 mL) were topically applied to each individual steer on their nuchal skin area. Steers were allocated to 1 of 24 drylot pens (12 pens/treatment) and received a free-choice diet until day 46. Steers were assessed daily for bovine respiratory disease (BRD) signs, and feed intake was recorded from each pen daily. Steer unshrunk BW was recorded on days 7, 17, 31, 45, and 46. Shrunk BW on day 0 was added an 8% shrink to represent initial BW, and final BW was calculated by averaging BW from days 45 and 46. Blood samples were collected from 5 steers/ pen on days 0, 7, 11, 31, and 45. Pen was considered the experimental unit. Steer BW gain was greater (P = 0.04) in BAS vs. CON (1.01 vs. 0.86 kg/d, SEM = 0.05). Feed intake did not differ (P = 0.95) between treatments, resulting in greater (P = 0.05) feed efficiency in BAS vs. CON (171 vs. 142 g/kg, SEM = 10). Plasma cortisol concentration was greater (P = 0.05) and plasma glucose concentration was less in CON vs. BAS on day 7 (treatment × day; P = 0.07 and <0.01, respectively). Mean plasma β-hydroxybutyrate concentration was greater (P < 0.01) in BAS vs. CON (3.23 and 2.75 mg/mL; SEM = 0.12). Incidence of BRD was greater (P ≤ 0.05) in BAS vs. CON from days 6 to 10 and days 19 to 23 (treatment × day; P < 0.01), although overall BRD incidence did not differ (P = 0.20) between treatments (82.4% vs. 76.6%, respectively; SEM = 3.2). A greater proportion (P = 0.04) of BAS steers diagnosed with BRD required one antimicrobial treatment to regain health compared with CON (59.3% vs. 47.6%, SEM = 4.2). Hence, BAS administration to steers upon feedlot arrival improved BW gain during a 45-d receiving period by enhancing feed efficiency. Moreover, results suggest that BAS improved steer performance by facilitating early detection of BRD signs, lessening the disease recurrence upon first antimicrobial treatment. [ABSTRACT FROM AUTHOR]

Economically relevant traits are routinely collected within the commercial segments of the beef industry but are rarely included in genetic evaluations because of unknown pedigrees. Individual relationships could be resurrected with genomics, but this would be costly; therefore, pooling DNA and phenotypic data provide a cost-effective solution. Pedigree, phenotypic, and genomic data were simulated for a beef cattle population consisting of 15 generations. Genotypes mimicked a 50k marker panel (841 quantitative trait loci were located across the genome, approximately once per 3 Mb) and the phenotype was moderately heritable. Individuals from generation 15 were included in pools (observed genotype and phenotype were mean values of a group). Estimated breeding values (EBV) were generated from a single-step genomic best linear unbiased prediction model. The effects of pooling strategy (random and minimizing or uniformly maximizing phenotypic variation within pools), pool size (1, 2, 10, 20, 50, 100, or no data from generation 15), and generational gaps of genotyping on EBV accuracy (correlation of EBV with true breeding values) were quantified. Greatest EBV accuracies of sires and dams were observed when there was no gap between genotyped parents and pooled offspring. The EBV accuracies resulting from pools were usually greater than no data from generation 15 regardless of sire or dam genotyping. Minimizing phenotypic variation increased EBV accuracy by 8% and 9% over random pooling and uniformly maximizing phenotypic variation, respectively. A pool size of 2 was the only scenario that did not significantly decrease EBV accuracy compared with individual data when pools were formed randomly or by uniformly maximizing phenotypic variation (P > 0.05). Pool sizes of 2, 10, 20, or 50 did not generally lead to statistical differences in EBV accuracy than individual data when pools were constructed to minimize phenotypic variation (P > 0.05). Largest numerical increases in EBV accuracy resulting from pooling compared with no data from generation 15 were seen with sires with prior low EBV accuracy (those born in generation 14). Pooling of any size led to larger EBV accuracies of the pools than individual data when minimizing phenotypic variation. Resulting EBV for the pools could be used to inform management decisions of those pools. Pooled genotyping to garner commercial-level phenotypes for genetic evaluations seems plausible although differences exist depending on pool size and pool formation strategy. [ABSTRACT FROM AUTHOR]

This study evaluated the effects of supplementing dry live yeast (LY ; Saccharomyces cerevisiae) on in vitro gas production (IVGP) fermentation dynamics, pH, and CH4 concentration at 48 h, and in situ rumen parameters and digestibility of DM (DMD) and NDF (NDFD) of growing cattle during 3 feeding phases: grower (GRW) for 17 d (38% steamed-flaked corn; SFC), transition (TRANS) for 15 d (55.5% SFC: 1.2 Mcal/kg NEg), and finisher (FIN) for 13 d (73% SFC: 1.23 Mcal/kg NEg). Twenty British-crossbred, ruminally cannulated steers (183 kg ± 44 kg) 6 mo of age were blocked by weight into 5 pens containing Calan gate feeders and received a control (CON) diet (17.2% CP, 35.8% NDF, 86.7% DM) without LY on days −12 to 0. After that, animals were randomly assigned to treatments (TRT), 5 animals per TRT: CON or LY at inclusion rates of 5 g/d (LY1), 10 g/d (LY2), or 15 g/d (LY3) top dressed every morning at 0800 for 45 d. The DMD and NDFD were assessed during 7 separate collection days using in situ nylon bags containing 5 g of GRW, TRANS, or FIN diets, incubated at 1200 for 48 h. Protozoa counts (PC) were determined during 5 collection periods. Data were analyzed as a repeated measure within a randomized complete block design, assuming a random effect of the pen. For GRW, TRT altered the total gas production of the nonfiber carbohydrate (NFC ; P = 0.045) and the fractional rate of degradation (kd) of the fiber carbohydrate (FC) pool (P = 0.001) in a cubic pattern (P ≤ 0.05): LY2 had the most gas production and fastest kd. TRT also influenced DMD (P = 0.035) and NDFD (P = 0.012) with LY2 providing the greatest digestibility. For TRANS, TRT tended to affect the NFC kd (P = 0.078) and influenced pH (P = 0.04) and DMD (P < 0.001) in which LY2 yielded the fastest kd, highest pH, and greatest DMD. For FIN, there was an effect of TRT on total gas production (P < 0.001) and kd (P = 0.004) of the NFC pool, FC kd (P = 0.012), in vitro CH4 concentration (P < 0.001), PC (P < 0.001), DMD (P = 0.039), and NDFD (P = 0.008). LY1 had the highest PC and provided the greatest DMD and NDFD. LY2 had the fastest kd of both the NFC and FC pools and had the least CH4 concentration. LY3 had the greatest NFC gas production. No specific dose–response pattern was observed, but 10 g/d provided the most beneficial result for all diets. We concluded that supplementation with LY affected IVGP as well as ruminal parameters and digestibilities. [ABSTRACT FROM AUTHOR]

This study utilized 204 Angus-based beef steers (249 ± 23 kg SD) from a single ranch with initial serum α-tocopherol concentrations of 3.9 ± 1.0 mg/L to determine the effect of varying doses of vitamin E (VE) on feedlot performance, antibody response to vaccination, and antioxidant defense. Seven days after arrival, steers were blocked by body weight and weaning protocol (preweaned, unweaned heavy, and unweaned light) and randomly assigned to pens within blocks (12 pens per block). Preweaned steers had been weaned for approximately 35 d prior to arrival, and unweaned steers were weaned when leaving the origin ranch. Pens within block were randomly assigned to supplemental VE (ROVIMIX E-50 Adsorbate, DSM Nutritional Products, Heerlen, The Netherlands) treatments (n = 9 pens per treatment): no supplemental VE (CON), 25 IU/kg dry matter (DM ; LOW), 500 IU per steer daily (MED), or 1,000 IU per steer daily (HIGH). Back-calculated supplemental VE intake was 0, 151 (24.8 IU/kg DM), 484, and 995 IU/d for CON, LOW, MED, and HIGH, respectively. On day 6, all steers received a booster vaccine against bovine viral diarrhea virus (BVDV ; Bovi-Shield Gold, One Shot, Zoetis, Parsippany, NJ). Steers were weighed on day −1, 0, 14, 26, and 27. One steer per pen representative of the average body weight of the pen was chosen as a sampling animal for blood (day −1, 6, 14, 26, and 28) and liver (day −3 and 24). Data were analyzed as a randomized complete block design using Proc Mixed of SAS with pen as the experimental unit and the fixed effects of treatment and block. Linear, quadratic, and cubic contrast statements were constructed using Proc IML; morbidity data were analyzed using Proc Glimmix. Day 24 liver and day 26 serum α-tocopherol concentrations were linearly increased by supplemental VE (P < 0.01). Supplemental VE did not affect DM intake, average daily gain, or gain:feed from day 0 to 27 (P ≥ 0.37), or the percentage of steers treated for respiratory disease (P ≥ 0.44). Day 24 liver glutathione concentrations decreased linearly due to supplemental VE (P ≤ 0.02). Total- and Mn-superoxide dismutase activities were quadratically affected by supplemental VE (P ≤ 0.07), with MED steers exhibiting the greatest activity. Over time, BVDV type 1 and 2 antibody titers numerically decreased, whereas the decrease in BVDV type 1 titers was lesser for HIGH steers (linear P = 0.04). Increasing doses of VE improved VE status but did not affect overall receiving period performance in steers with minimal to adequate VE status upon arrival. [ABSTRACT FROM AUTHOR]

The objectives of this study were to assess the effects of Saccharomyces cerevisiae fermentation products (SCFP ; NaturSafe, SCFPns ; and Original XPC, XPC ; Diamond V) on growth performance, carcass traits, immune response, and antimicrobial resistance in beef steers fed high-grain diets. Ninety Angus steers (initial body weight [BW], 533 ± 9.8 kg) were assigned to a randomized complete design with 6 treatments (n = 15/treatment): 1) control, 2) low (12 g SCFPns·steer−1·d−1), 3) medium (15 g SCFPns·steer−1·d−1), 4) high SCFP (18 g SCFPns·steer−1·d−1), 5) encapsulated XPC (eXPC ; 7 g XPC·steer−1·d−1 encapsulated with 9 g capsule material), and 6) antibiotics (ANT ; 330 mg monensin + 110 mg tylosin·steer−1·d−1). Steers were fed ad libitum a diet containing 10% barley silage and 90% barley grain concentrate mix (dry matter basis) for 105 d. Increasing SCFPns tended (P < 0.09) to linearly increase feed efficiency. Average daily gain (ADG) tended (P < 0.10) to be greater in steers supplemented with eXPC than control. The SCFPns also tended (P < 0.10) to linearly increase marbling score. Proportion of severely abscessed livers tended (P < 0.10) to be lower in steers supplemented with medium and high SCFPns, eXPC, or ANT. A treatment × days on feed interaction were noticed (P < 0.01) for blood glucose, blood urea nitrogen (BUN), and acute phase proteins. The concentration of blood glucose responded quadratically (P < 0.05) on days 28 and 56, whereas BUN linearly (P < 0.01) increased on day 105 with increasing SCFPns dose. The SCFPns linearly increased haptoglobin (P < 0.03) and serum amyloid A (SAA; P < 0.05) concentrations on day 105, and lipopolysaccharide binding protein (LBP; P < 0.01) on days 56 and 105. The percentage of erythromycin-resistant and erythromycin + tetracycline-resistant enterococci was greater (P < 0.05) with ANT than control, SCFPns, and eXPC, whereas no difference was observed among control, SCFPns, and eXPC. No treatment effect was detected on the percentage of tetracycline-resistant enterococci. These results indicate that feeding SCFPns and eXPC was beneficial in improving ADG, feed efficiency and decreasing liver abscesses in a manner comparable to ANT. Unlike antibiotics, SCFPns or eXPC did not increase antimicrobial resistance. Both SCFPns and eXPC are potential alternatives to in-feed antibiotics. [ABSTRACT FROM AUTHOR]

The increasing global population, limited resource availability, and global focus on reducing greenhouse gas (GHG) emissions put pressure on animal agriculture industries to critically evaluate and optimize the role they play in a sustainable food production system. The objective of this review is to summarize evidence of the various roles that the U.S. beef industry plays in the U.S. and global agricultural systems. As the world's largest beef producer, the United States reaps considerable economic benefit from the beef industry through strong domestic and international demand, as well as employment opportunities for many Americans. Beef production contributes to GHG emissions, land use, and water use, among other critical environmental impacts but provides an important source of essential micronutrients for human consumption. The U.S. beef industry provides sufficient product to meet the protein, vitamin B12, omega-3 and -6 fatty acid requirements of 43, 137, 47, and 487 million people, respectively. In the United States, beef production was estimated to account for 53% of GHG emissions from U.S. animal agriculture and 25% of GHG emissions from all of U.S. agriculture. Footprinting studies suggest that much of the land use and water use associated with beef production are attributed to the development of feed crops or pastureland. On a global scale, beef from U.S. origin is exported to numerous developed and developing countries, representing an important international nutrient routing. Along with other prominent beef-producing nations, the United States continues to pursue a greater level of sustainability in its cattle industry, which will bear important implications for future global food security. Efforts to reduce the environmental impacts of beef production will likely be the strongest drivers of enhanced sustainability. [ABSTRACT FROM AUTHOR]

Residual energy intake (REI) on two successive diets (hay and maize based) and slaughter traits, including visceral organs, were phenotyped in 584 adult purebred Charolais cows. To investigate the relationships between these traits and their genetic determinism, we first estimated the genetic parameters, including correlations, using REML modeling under WOMBAT software. The animals were then genotyped on the BovineSNP50 SNPchip before being imputed to the 600K density and genome wide association study was performed with GCTA software. We found low heritability for REI (h 2 = 0.12 in each of the diet phases). Although the phenotypic correlation between the two diet phases was moderate (0.36), the genetic correlation was high (0.83), indicating a common genetic determinism for feed efficiency regardless of the diet. Correlations between REI and slaughter traits were negative regarding muscle-related traits and positive for fat-related traits, indicating that efficient animals generally had a more muscular carcass. It was also seen that feed efficiency was genetically and phenotypically correlated with smaller organs when expressed as a proportion of their empty body weight. From the GWAS analysis, seven QTLs were found to be associated with a trait at the genome-wide level of significance and 18 others at the chromosome-wide level. One important QTL was detected in BTA 2, reflecting the essential effect of the myostatin gene on both carcass composition and relative organ weight. Three QTLs were detected for REI during the maize diet phase on BTA 13, 19, and 28, the latter being significant at the genome-wide level. The QTLs on BTA 19 mapped into the TANC2 gene and the QTLs on BTA 28 into the KIF1BP gene, which are both known to interact with the same protein (KIF1A). However, no obvious functional link between these genes and feed efficiency could be made. Among the other QTLs detected, one association on BTA 4 with liver proportion mapped to the candidate gene WASL , which has previously been shown to be differentially expressed in liver cells and linked to feed restriction or cancer development. No QTLs were found to be common between feed efficiency and any slaughter traits. [ABSTRACT FROM AUTHOR]

Previous research has determined that maintaining young animals in stalls is detrimental to their bone health, while the addition of 50 to 82-m sprints 5 d/week aids in counteracting the reduction of bone strength from confinement. The current research aims to determine if 1 or 3 d/week of sprinting affords the same benefits to bone as 5 d/week of sprinting compared to animals confined with no sprinting. Twenty-four Holstein bull calves were obtained from the Michigan State University Dairy Cattle Teaching and Research Center. At 9 wk of age, calves were randomly assigned to treatments of 1, 3, or 5 d/week of sprint exercise, or to the confined control group sprinted 0 d/week. Each treatment had 6 calves. Individual sprinting bouts included a single sprint down a 71-m concrete aisle. For the duration of the 6-wk study, calves were housed at the MSU Beef Cattle Teaching and Research Center in stalls which afforded calves room to stand, lay down, and turn around. Serum was collected weekly via jugular venipuncture to obtain concentrations of osteocalcin (OC) and C-telopeptide crosslaps of type I collagen (CTX-1)—markers of bone formation and degradation, respectively. Sprints were videotaped weekly to determine stride frequency and sprint velocity. On day 42, calves were humanely euthanized at the Michigan State University Meat Lab and both front limbs were immediately harvested. Computed tomography scans and mechanical testing were performed on the left fused third and fourth metacarpal bones. Serum OC concentration was greatest for calves sprinted 5 d/week (P < 0.001). Calves sprinted 5 d/week had both greater stride frequency (P < 0.05) and lower sprint velocity (P < 0.05). All exercise treatments experienced greater dorsal cortical widths compared to control animals (P < 0.01). Through mechanical testing, fracture forces of all sprinting treatments were determined to be greater than the control treatment (P < 0.02). Results from this study support that sprinting 1, 3, or 5 d/week during growth can increase bone health and cause favorable alterations in bone markers. While all exercise treatments had over a 20% increase to fracture force, calves sprinted 1 d/week sprinted only 426 m over the 6-wk study and still experienced over a 20% increase in bone strength compared to confined calves. This study demonstrates the remarkably few strides at speed needed to enhance bone strength and emphasizes the danger to skeletal strength if sprinting opportunities are not afforded. [ABSTRACT FROM AUTHOR]

Thermal stress in hot humid conditions limits cattle production. The objectives for this study were to estimate genetic parameters for hair characteristics and core body temperature under low and high temperature humidity index (THI) conditions. Hair samples were collected and measured for length and diameter. Core body temperature was measured as vaginal temperature every 15 min over a 5-d period using an iButton temperature measuring device implanted in a blank CIDR in 336 heifers from the University of Florida multibreed herd (ranging from 100% Angus to 100% Brahman). Restricted maximum likelihood procedures were used to estimate heritabilities from multiple bivariate animal models using the WOMBAT program. Estimates of heritability for hair diameter, undercoat length, topcoat length, body temperature under low THI conditions, and body temperature under high THI conditions were 0.50, 0.67, 0.42, 0.32, and 0.26, respectively. The genetic parameters estimated in this study indicate a large, exploitable genetic variance which can be selected upon to improve tolerance in cattle. Breed effects for differing compositions of Brahman and Angus were also estimated. As Brahman breed composition increased by 25% undercoat length, topcoat length, body temperature under low THI conditions, and body temperature under high THI conditions decreased by 1.32 mm, 2.94 mm, 0.11 °C, and 0.14 °C, respectively. Under both low and high THI conditions, cattle with 25% Brahman breed composition or greater maintained a significantly lower body temperature than the 100% Angus breed group. The incorporation of Brahman germplasm is recommended for herds that often experience heat stress conditions in order to increase resilience to heat stress. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine whether feeding tannin-containing hays to heifers and mature beef cows influences enteric methane (CH4) emissions and nitrogen (N) excretion relative to feeding traditional legume and grass hays. Fifteen mature beef cows (Exp. 1) and 9 yearling heifers (Exp. 2) were each randomly assigned to treatment groups in an incomplete bock design with 2 periods and 6 types of hays with 3 hays fed each period (n = 5 cows and 3 heifers per treatment). Groups were fed tannin-containing [birdsfoot trefoil (BFT), sainfoin (SAN), small burnet (SML)] or non-tannin-containing [alfalfa (ALF), cicer milkvetch (CMV), meadow bromegrass (MB)] hays. Each period consisted of 14 d of adjustment followed by 5 d of sample collection. Nine cows and 9 heifers were selected for the measurement of enteric CH4 emissions (sulfur hexafluoride tracer gas technique), and excretion of feces and urine, while dry matter intake (DMI) was measured for all animals. The concentration of condensed tannins in SAN and BFT was 2.5 ± 0.50% and 0.6 ± 0.09% of dry matter (DM), respectively, while SML contained hydrolyzable tannins (4.5 ± 0.55% of DM). Cows and heifers fed tannin-containing hays excreted less urinary urea N (g/d; P < 0.001) and showed lower concentrations of blood urea N (mg/dL; P < 0.001) than animals fed ALF or CMV, indicating that tannins led to a shift in route of N excretion from urine to feces. Additionally, cows fed either BFT or CMV showed the greatest percentage of retained N (P < 0.001). Enteric CH4 yield (g/kg of DMI) from heifers (P = 0.089) was greatest for MB, while daily CH4 production (g/d) from heifers (P = 0.054) was least for SML. However, digestibility of crude protein was reduced for cows (P < 0.001) and heifers (P < 0.001) consuming SML. The results suggest that tannin-containing hays have the potential to reduce urinary urea N excretion, increase N retention, and reduce enteric CH4 emissions from beef cattle. The non-bloating tannin-free legume CMV may also reduce environmental impacts relative to ALF and MB hays by reducing N excretion in urine and increasing N retention. [ABSTRACT FROM AUTHOR]

The goal of this study was to compare the cell-mediated immune responses of highly commingled, sale-barn origin calves (STR ; n = 10) to those of single source calves that had been weaned for 60 d (UNS ; n = 10). Peripheral blood mononuclear cells and neutrophils (PMNs) were isolated from jugular venous blood of each calf. Peripheral blood mononuclear cells were stimulated with Concanavalin A (ConA), BVDV-1, BVDV-2, BHV-1, Mannheimia haemolytica , and Pasteurella multocida and evaluated for clonal proliferation and secretion of IL-8 into cell culture supernatants. The native functional capacities of PMNs were evaluated in response to stimulation with heat-killed Escherichia coli and Staphylococcus aureus. Complete blood counts and serum biochemical profiles were performed for each animal at the time of sample collection. Compared with STR calves, UNS calves had greater lymphocyte proliferative responses following stimulation BVDV1 (P = 0.041), BVDV2 (P = 0.002), BHV-1 (P = 0.001), M. haemolytica (P = 0.016), and P. multocida (P = 0.049). In addition, PMNs isolated from UNS calves had a greater ability to phagocytose E. coli (P = 0.001) and S. aureus (P = 0.003) when compared with STR calves. Serum nonesterified fatty acids were higher in STR calves (P < 0.001). Serum β-hydroxybutyrate was lower in STR calves (P < 0.003). These data suggest that immunologic and physiologic differences exist between STR and UNS calves. Although the underlying mechanisms for these differences are not clear, it is possible that combinations of energy imbalances, stress-induced immunosuppression, and general immune naiveté may predispose STR calves to an increased risk of morbidity and mortality due to bovine respiratory disease. [ABSTRACT FROM AUTHOR]

The objective of this trial was to determine the benefits of supplementing active dried yeast (ADY ; 3 × 1010 CFU/d of Saccharomyces cerevisiae) in diets of growing and finishing steers on ruminal pH and liver health, and evaluate the relationship of these variables with performance traits. Growing beef steers (n = 120) were blocked by weight (i.e. heavy and light) and allocated to 1 of 4 pens in an automated feed intake monitoring system. Steers were fed either control (CON ; no ADY) or ADY supplemented in 4 sequential diets: grower diet from days 0 to 70, 2 step up diets (STEP1 and STEP2) for 7 d each, and finishing diet from days 85 to 164. Indwelling rumen boli were administered to monitor rumen pH during days 56 to 106 during the dietary transition. An exchange of pen assignment, within block, occurred on day 70 resulting in 4 final treatment (TRT) assignments: steers fed CON before and after the exchange (CC ; n = 30), steers fed CON before and ADY after the exchange (CY ; n = 30), steers fed ADY before and CON after the exchange (YC ; n = 30), and steers fed ADY (YY ; n = 30). Ruminal parameters were analyzed as a randomized complete block design with repeated measures of day, diet and TRT as fixed effects, and block as random effects, using 2 approaches: preliminary analysis of the means or drift analysis (DA ; units change from basal values over time). Ruminal pH duration (DUR) below 6.0 (P = 0.05) and 5.8 (P = 0.05) was greater for CY steers than CC steers. Acidosis bout prevalence (pH < 5.6 for 180 consecutive minutes; P < 0.01) and bout DUR (P = 0.05) were greater for CY than other TRT groups. The DA indicated that the ruminal pH variables range, variance, and amplitude of steers in the YC group drifted further from basal pH values than CY and YY steers during the dietary transition (P ≤ 0.02), indicating that removing ADY during the dietary transition was not favorable, but including ADY may reduce ruminal fluctuation. Steers with fewer days experiencing bouts (DEB) had numerically greater ADG (P = 0.11) and tended to have greater G:F (P = 0.06). Liver abscess severity negatively affected ADG (P = 0.04). However, liver abscess severity was not affected by DEB (P = 0.90). There is evidence to suggest that the addition of the specific ADY strain in the diets of beef cattle during the dietary transition may aid in ruminal stabilization, but our study did not find evidence that acidosis bouts were related to abscess prevalence or severity. [ABSTRACT FROM AUTHOR]

Developing accurate genomic evaluations of fertility for tropical beef cattle must deal with at least two major challenges (i) recording cow fertility traits in extensive production systems on large numbers of cows and (ii) the genomic evaluations should work across the breeds, crossbreds, and composites used in tropical beef production. Here, we assess accuracy of genomic evaluations for a trait which can be collected on a large scale in extensive conditions, corpus luteum score (CLscore), which is 1 if ovarian scanning indicates a heifer has cycled by 600 d and 0 if not, in a multi-breed population. A total of 3,696 heifers, including 979 Brahmans, 914 Droughtmasters, and 1,803 Santa Gertrudis in seven herds across 3-yr cohorts with CLscores, were genotyped for 24,211 SNPs. Genotypes were imputed to 728,785 SNPs. GBLUP and BayesR were used to predict GEBV. Accuracy of GEBV was evaluated with two validation strategies. In the first strategy, the last year cohort of heifers from each herd was used for validation, such that every herd had heifers in both reference and validation populations. In the second validation strategy, each herd in turn was removed in its entirety from the reference population, and was used for validation. For both validation strategies, accuracy of GEBV for single breed and multi-breed reference populations was assessed. For the first validation strategy, accuracy of GEBV ranged from 0.2 for Brahmans to 0.4 for Droughtmasters. Increasing marker density from 24K SNPs to 728K SNPs resulted in a small increase in accuracy, and including multiple-breeds in the reference did not help improve accuracy. These results suggest that provided a herd has animals in the reference population, the accuracy of the GEBV is largely determined by within herd (linkage) information. The situation was very different when entire herds were predicted in the second validation. In this case accuracy of GEBV using only 24K SNPs and only a within breed reference was close to zero for all breeds. Accuracy increased substantially when 728K SNPs, BayesR, and a multi-breed reference were used, from 0.15 for Brahmans to 0.35 for Santa Gertrudis. Given the second validation strategy is more likely to reflect the situation for many herds in tropical beef production (no animals in the reference), genomic evaluations for fertility in tropical beef cattle should be based on high-density markers (728K SNPs) and should be multi-breed. [ABSTRACT FROM AUTHOR]

This experiment evaluated the effects of supplementing a saponin-containing feed ingredient, manufactured from purified extract of Yucca schidigera [Micro-Aid (MA); DPI Global; Porterville, CA], on performance, health, and physiological responses of receiving cattle. A total of 105 recently weaned Angus x Hereford calves (75 steers and 30 heifers), originating from eight cow-calf operations, were obtained from an auction facility on day −2 and road transported (800 km; 12 h) to the experimental facility. Immediately after arrival on day −1, shrunk BW was recorded and calves were grouped with free-choice access to grass hay, mineral supplement, and water. On day 0, calves were ranked by sex, source, and shrunk BW, and allocated to one of 21 pens (5 calves/pen; being one or two heifers within each pen). Pens were assigned to receive a total mixed ration (TMR) and one of three treatments (as-fed basis): (1) 1 g/calf daily of MA (M1 ; n = 7), (2) 2 g/calf daily of MA (M2 ; n = 7), or (3) no MA supplementation (CON ; n = 7). Calves received the TMR to yield 15% (as-fed basis) orts, and treatments were top-dressed from days 0 to 59. Calves were assessed for bovine respiratory disease (BRD) signs and TMR intake was recorded for each pen daily. Calves were vaccinated against BRD pathogens on days 0 and 21. Final shrunk BW was recorded on day 60, and blood samples were collected on days 0, 2, 6, 10, 14, 21, 28, 34, 45, and 59. ADG was greater (P = 0.03) in M2 vs. M1 and CON (1.53, 1.42, and 1.42 kg/day, respectively), and similar (P = 0.95) between M1 and CON calves. No treatment effects were detected for TMR intake (P = 0.52), whereas feed efficiency was greater (P ≤ 0.05) in M2 vs. M1 and CON calves (213, 200, and 204 g/kg, respectively) and similar (P = 0.40) between M1 and CON calves. No treatment effects were detected (P = 0.39) for diagnosis of BRD signs. The number of antimicrobial treatments required upon BRD diagnosis was greater (P ≤ 0.01) in CON vs. M1 and M2 (1.40, 1.05, and 1.10 treatments, respectively), and similar (P = 0.60) between M1 and M2 calves. No other treatment effects were detected (P ≥ 0.23), including circulating concentrations of hormones and metabolites, serum antibody titers to BRD pathogens, and mRNA expression of innate immunity genes in whole blood. Collectively, results from this experiment suggest that MA supplementation at 2 g/animal daily enhances performance and response to BRD treatment in high-risk cattle during feedlot receiving. [ABSTRACT FROM AUTHOR]

The objective of the study was to determine whether oversupplying MP prepartum affects postpartum cow BW, colostrum composition, milk production and composition, protein catabolism in the dam, and calf growth. Crossbred Hereford heifers were individually fed a control treatment designed to meet MP requirements (CON ; n = 10) or 133% of the MP requirement (HMP ; n = 11) from day −55 ± 4 until parturition. All cows were provided a common postpartum diet. Cow BW was measured on days 7 ± 1, 14 ± 2, 28 ± 3, 57 ± 4, 82 ± 5, and 111 ± 3 relative to parturition. DMI and ruminal pH were measured daily and summarized by week until day 33. Milk yield was estimated based on a 12-h two-quarter milk yield on days 7 ± 1, 12 ± 1, 28 ± 3, 33 ± 3, 70 ± 3, and 112 ± 3. Urine samples were collected from cows over a 6-d period starting on days 7 ± 1 and 28 ± 3 and the composited samples were analyzed for 3-methylhistidine (3-MH) and creatinine. Muscle samples were collected from cows on day 13 ± 1 while calf muscle samples were collected on days 2 and 111 ± 3 of age. Muscle samples from cows were analyzed for markers of protein catabolism, and calf muscle samples were analyzed for genes regulating cell growth and differentiation. Data were analyzed as a randomized complete block design using the MIXED procedure of SAS accounting for repeated measures when necessary. Postpartum BW did not differ (P ≥ 0.30) by treatment, day, or the interaction of treatment and day (T × D), but rump fat decreased (P = 0.011) as lactation progressed. DMI decreased during weeks 2 and 3 compared to 1 and 4, whereas ruminal pH was less during weeks 2, 3, and 4 relative to week 1. Colostrum fat concentration was less (P = 0.003) for HMP than CON; but, milk production was not affected by treatment. Milk yield was greatest from days 7 to 33 and decreased thereafter (P < 0.01). Urinary 3-MH and the 3-MH:creatinine ratio did not differ by treatment, day, or the T × D (P ≥ 0.22) interaction, nor was there a difference (P ≥ 0.13) in the abundance of catabolic proteins. Calf growth was not affected by treatment, but HMP calves had greater expression (T × D, P = 0.05) of PPARG while PKM expression increased for CON calves (T × D, P = 0.04) at day 111 compared to their expression at day 2. Overfeeding MP during late gestation does not improve postpartum indicators of N balance or maternal muscle turnover but may alter colostrum composition and calf gene expression at weaning. [ABSTRACT FROM AUTHOR]

The objective of the study was to determine the effect of oversupplying MP during late gestation on maternal BW, ruminal fermentation, nitrogen balance, and skeletal muscle catabolism. Crossbred Hereford heifers (n = 24) were assigned to a control treatment designed to meet MP requirements (CON) or a treatment providing 133% of the MP requirement (HMP). Heifers were individually fed their treatment from day −55 ± 3 relative to parturition and DMI was summarized by week. BW was measured on day −55 ± 3, −41 ± 3, −27 ± 3, and −8 ± 3. Ruminal digesta samples were collected on day −34 ± 5 and −15 ± 4 for short-chain fatty acid and ammonia-N (NH 3 -N) concentration. Plasma was collected the day prior to ruminal digesta samples and analyzed for plasma urea-N. Nitrogen balance was measured over a 6-d period starting on day −34 ± 4 and −15 ± 4. Following completion of the N balance periods, muscle biopsies were collected from the longissimus dorsi and analyzed for abundance of proteins relating to skeletal muscle catabolism. Data were analyzed as a randomized complete block (date of parturition) design with repeated measures using the MIXED procedure of SAS. Heifers fed HMP increased conceptus-corrected BW by a greater magnitude than CON at day −8 relative to −55 and −41 (treatment × day, P < 0.01). DMI increased (P < 0.01) by 18% on week −2 compared to −8, but then decreased (P < 0.01) by 8.0% for week −1. N-intake, apparent N digestion, N excretion, and N retention (g/d) were all greater (P < 0.01) for HMP heifers than CON but did not differ when expressed as a proportion of N intake. Ruminal NH3-N decreased (treatment × day, P < 0.01) as parturition approached for HMP (10.1 to 8.6 mg/dL); whereas, NH3-N was not affected for CON (1.0 to 1.3 mg/dL). Consequently, plasma urea-N was greater (P < 0.01) for HMP heifers (15.0 vs. 7.5 mg/dL). Heifers fed HMP had improved (P < 0.01) DM, OM, and NDF digestibility relative to CON heifers. The abundance of calpastatin was greater (P = 0.03) and calpain tended to be greater (P = 0.085) for CON cows compared to HMP. Feeding greater quantities of MP during late gestation may improve ruminal fermentation, N balance, and improve BW gain prepartum. [ABSTRACT FROM AUTHOR]

Heifers that have an earlier age at puberty often have greater lifetime productivity. Age at puberty is moderately heritable so selection should effectively reduce the number of days to puberty, and improve heifer productivity and profitability as a result. However, recording age at puberty is intensive, requiring repeat ovarian scanning to determine age at first corpus luteum (AGECL). Genomic selection has been proposed as a strategy to select for earlier age at puberty; however, large reference populations of cows with AGECL records and genotypes would be required to generate accurate GEBV for this trait. Reproductive maturity score (RMS) is a proxy trait for age at puberty for implementation in northern Australia beef herds, where large scale recording of AGECL is not feasible. RMS assigns a score of 0 to 5 from a single ovarian scan to describe ovarian maturity at ~600 d. Here we use multivariate genomic prediction to evaluate the value of a large RMS data set to improve accuracy of GEBV for age at puberty (AGECL). There were 882 Brahman and 990 Tropical Composite heifers with AGECL phenotypes, and an independent set of 974 Brahman, 1,798 Santa Gertrudis, and 910 Droughtmaster heifers with RMS phenotypes. All animals had 728,785 real or imputed SNP genotypes. The correlation of AGECL and RMS (h 2 = 0.23) was estimated as −0.83 using the genomic information. This result also demonstrates that using genomic information it is possible to estimate genetic correlations between traits collected on different animals in different herds, with minimal or unknown pedigree linkage between them. Inclusion of heifers with RMS in the multi-trait model improved the accuracy of genomic evaluations for AGECL. Accuracy of RMS GEBV generally did not improve by adding heifers with AGECL phenotypes into the reference population. These results suggest that RMS and AGECL may be used together in a multi-trait prediction model to increase the accuracy of prediction for age at puberty in tropically adapted beef cattle. [ABSTRACT FROM AUTHOR]

Genetic and phenotypic parameters for feed efficiency, growth, and carcass traits for Australian Angus beef cattle were estimated. Growth traits included birth weight (BWT), 200-d weight (200dWT), 400-d weight (400dWT), and 600-d weight (600dWT). Traits associated with feed efficiency were average daily weight gain (ADG), metabolic midweight, average of daily feed intake (FI), feed conversion ratio (FCR), residual feed intake (RFI), and residual gain (RG). Carcass traits involved were carcass eye muscle area (CEMA), carcass intramuscular fat (IMF), subcutaneous fat depths at the 12th/13th rib (CRIB), rump P8 fat depth (P8FAT), and carcass weight (CWT). For growth traits, heritability estimates ranged from 0.14 ± 0.03 for 200dWT to 0.48 ± 0.06 for 600dWT. For feed efficiency traits, direct heritability estimates for FI, FCR, RFI, and RG were 0.55 ± 0.08, 0.20 ± 0.06, 0.40 ± 0.07, and 0.19 ± 0.06, respectively. High heritability estimates were observed for CEMA, IMF, P8FAT, and CWT of 0.52 ± 0.09, 0.61 ± 0.09, 0.55 ± 0.09, and 0.66 ± 0.09, respectively. Strong positive genetic correlations were found for FI with 200dWT, 400dWT, and 600dWT of 0.68 ± 0.09, 0.42 ± 0.11, and 0.61 ± 0.07, respectively. Weak genetic correlations were observed between RFI and growth traits. For carcass traits, genetic correlations between RFI and CEMA, IMF, CRIB, P8FAT, CWT were −0.19 ± 0.14, 0.31 ± 0.14, 0.18 ± 0.16, 0.24 ± 0.13, and 0.40 ± 0.12, respectively. There was a tendency for low to moderate unfavorable genetic associations between feed efficiency traits, evaluated as RFI and RG, with growth and carcass traits. This implies that selection for RFI would have slight negative impacts on growth and reduce carcass quality. To avoid this, it would be necessary to build selection indices to select feed efficient animals without compromising growth and meat quality. [ABSTRACT FROM AUTHOR]

Models of energy utilization used in livestock production predict input:output relationships well, for all the wrong reasons. Predictive accuracy in such models is not due to fidelity to biochemistry and laws of thermodynamics, but because they were developed to predict accurately, often with little regard to biochemical consistency. Relatively static linear statistical models limit thermodynamically relevant descriptions of energy utilization, especially maintenance, in growing beef cattle and are inadequate research tools, in either ordinary least squares (OLS) or Bayesian frameworks. Metabolizable energy intake (MEI) at recovered energy (RE) = 0 (MEm) and efficiencies of ME utilization for maintenance (km) and gain (kg) were estimated for 3 independent data sets using OLS or Bayesian frameworks. Estimates of MEm differed (P < 0.05) between OLS and Bayesian estimates and were not unique, indicating model misspecification. Bayesian estimates of MEm were monotonic, positive, and nonlinear f(MEI); the range was from 6.74 to 14.8 Mcal/d. Estimates of km, the ratio of heat energy (HE) at MEI = 0 to MEm, for the 3 data sets averaged 0.590 for OLS solutions, or 0.616 for the first derivative (km, dHE/dMEI for RE = 0) of a first-order function. The first derivative (dHE/ dMEI) of the OLS function was > 1.0 for MEI > 22.1 Mcal/d, counter to the laws of thermodynamics and indicated model misspecification. The Bayesian estimate of km (0.420) differed (P < 0.05) from the OLS estimate and was consistent with the efficiency of ATP synthesis. Efficiency of ME use for gain for RE > 0 (kg, OLS solutions) averaged 0.397, solutions were nonunique and single-variable OLS models were misspecified (P < 0.050) for 2 of the 3 data sets. The OLS estimate of kg differed (P < 0.05) from the estimate of kg (0.676) determined in a Bayesian framework; the latter was calculated as dRE/dMEI for RE > 0. For OLS estimates km > kg; for estimates determined in a Bayesian framework km < kg, the former is inconsistent, while the latter is consistent with the thermodynamic favorability of reactions underlying maintenance and gain. Our results show that the use of relatively fixed coefficients of maintenance in current feeding standards, mathematical descriptions of metabolic processes and concepts regarding efficiencies of energy utilization in those systems need modification to be consistent with animal biology and the laws of thermodynamics. [ABSTRACT FROM AUTHOR]

An experiment was conducted to evaluate the fabrication yields of carcasses from beef steers supplemented zilpaterol hydrochloride (ZH) and fed at maintenance (MA) or ad libitum (AB) intake levels. Beef steers (n = 56) from a common sire were blocked (n = 28 per block) by terminal growth implant and sorted into pairs by BW. Four pairs (n = 8) were harvested on day 0; the remaining 24 pairs (n = 48) were assigned to a dietary intake level (MA or AB) and days on feed (28 or 56 d). Within pairs of MA or AB intakes, steers harvested on day 56 were randomly assigned to supplementation of ZH (90 mg·d-1 per steer) for 20 d followed by a withdrawal period of 4 d or control (C). Steers (BW = 603.5 ± 48.1 kg) were harvested at a commercial processing facility. After a 24-h chill period, standard USDA grading procedures were used to derive a calculated yield grade and quality grade. Following grading, left carcass sides were transported to the West Texas A&M University Meat Laboratory for fabrication. Each side was fabricated into subprimals to determine individual red meat yield (RMY), trimmable fat yield (TFY), and bone yield (BY). A mixed model was used for analysis; fixed effects included treatment combinations and random effects included block and pairs. Single df contrasts tested day 0 vs. 28, day 0 vs. 56, day 28 vs. 56, MA vs. AB, and C vs. ZH. Yield of chuck eye roll differed (P = 0.05) by days on feed (0 d = 4.14, 28 d = 4.11, 56 d = 4.55%). Similarly, eye of round yield was impacted (P = 0.02) by days on feed (0 d = 1.51, 28 d = 1.37, 56 d = 1.36%). Additionally, brisket yield was altered (P < 0.01) by days on feed (0 d = 4.08, 28 d = 3.56, 56 d = 3.48%) and treatment (C = 3.34, ZH = 3.61%). For remaining subprimals, no differences (P = 0.15) were detected. Furthermore, results indicated that RMY tended (P = 0.07) to differ by treatment (C = 61.35, ZH = 63.67%). Comparatively, TFY was impacted (P = 0.04) by intake (MA = 20.44, AB = 23.33%). Results from this study indicate that a MA intake level during the last 56 d of the finishing period concurrent with ZH supplementation impacts subprimal yields as well as carcass RMY and TFY of beef steers. [ABSTRACT FROM AUTHOR]

The objective of this trial was to determine the effects of supplementing active dried yeast (ADY) in the diets of finishing steers on energy and nitrogen metabolism and ruminal pH characteristics under thermoneutral (TN) or heatstressed (HS) conditions. Eight British cross steers received 1 of 2 treatments (TRT) [either a control finishing diet (CON) or supplemented with 3 g/d of ADY] under 1 of 2 temperatures [TEMP: TN = 18 ± 0.55 °C and 20 ± 1.2% relative humidity (RH) or HS = 35 ± 0.55 °C and 42 ± 6.1% RH]. Steers were orally administered an indwelling rumen pH and temperature recording bolus. Data collection occurred for 48 consecutive hours inside 2 calorimetry chambers. Data were analyzed as a 4 X 8 Latin rectangle design with fixed effects of TRT and TEMP and random effects of steer and period. There were no TRT X TEMP interactions for metabolism or calorimetric measurements (P ≥ 0.1510). In vivo DM digestibility (DMD) was greater for ADY-fed steers than for CON-fed steers (77.1% vs. 75.3%, respectively; P = 0.0311). No TRT (P = 0.3032) or TEMP (P = 0.1833) effect was observed for nitrogen retention. Energy partitioning suggested DE and ME (Mcal/kg) were greater for ADY-fed steers than for CON-fed steers (P = 0.0097 and P = 0.0377, respectively). Steers under HS had reduced DMI but greater DMD than TN steers (77.1% vs. 75.3%, respectively; P = 0.0316) and greater CH4 per unit of DM (8.53 vs. 6.47 g/kg, respectively; P = 0.0145). Although DE was greater for HS than TN (3.16 vs. 3.06 Mcal/kg, respectively; P = 0.0123), heat production energy (HE) tended to be greater for HS than TN (18.1 vs. 17.0 Mcal/d, respectively; P = 0.0743), resulting in a less retained energy (0.412 vs. 0.100 Mcal/kg; P = 0.0147). There was a tendency for an interaction of mean ruminal pH (P = 0.1279) where pH of ADY-fed steers was greater than pH of CON-fed steers under TN conditions (5.81 vs. 5.57, respectively), but not under HS conditions (5.37 vs. 5.41, respectively). Duration (DUR) and area under the curve (AUC) for pH > 5.6 had similar tendencies; under TN conditions, the DUR and AUC for pH > 5.6 in ADY-fed steers were greater than in CON-fed steers (P = 0.0726 and P = 0.0954, respectively), but under HS conditions, there was no difference between ADY and CON. We conclude that supplementing ADY in the diets of finishing steers improved DMD, DE, ME, and mean ruminal pH under TN conditions, but not in extreme HS conditions likely due to reduced DMI and greater HE requirements. [ABSTRACT FROM AUTHOR]