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The objectives of this study were to evaluate heat stress feed intake models for growing swine using a data set assembled from the literature and to develop a series of new equations modeling the influence of the thermal environment and interactions between the thermal environmental and other factors on feed intake. A literature survey was conducted to identify studies assessing intake responses to temperature. The resulting data set comprised 35 studies containing 120 comparisons to thermoneutral intake. Intake as a fraction of thermoneutral intake (FFI) was the primary response variable, where a value of 1 represented no change from thermoneutral intake. The FFI predicted by NRC and a recent model from a meta-analysis (Renaudeau et al.,) were compared to observed values. New parameters for the NRC equation (NRCmod) were derived, and a series of new equations incorporating duration of exposure (TD), temperature cycling (TC), and floor type (TH) were also derived. Root-mean-square prediction error (RMSPE) and concordance correlation coefficients were used to evaluate all models. The RMSPE for the NRC model was 23.6 with mean and slope bias accounting for 12.6% and 51.1% of prediction error, respectively. The TD, TC, and TH models had reduced RMSPE compared with NRC: 12.9 for TD, 12.6 for TC, and 12.9 for TS. Substantial improvements were also made by refitting parameters (NRCmod; RMSPE 13.0%). In NRCmod, TD, TC, and TH, random error was the predominant source, accounting for over 97% of prediction error. The Renaudeau et al. model was also evaluated. Renaudeau et al. had relatively low RMSPE (22.3) for intake but higher RMSPE for FFI (22.6) than NRC, NRCmod, TD, TC, or TH. Additional parameters were derived for the Renaudeau et al. equation to account for housing system and diet characteristics. This adjustment reduced RMSPE of predicting feed intake (16.0) and FFI (16.3) and reduced systematic bias in the equation. This evaluation of equations highlights the effects of novel explanatory variables on feed intake during heat stress, and the comparison can be useful when selecting a model that best explains variability in feed intake responses to heat stress given available input data. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess environmental impact, economic viability, and social acceptability of 3 beef production systems with differing levels of efficiency. A deterministic model of U.S. beef production was used to predict the number of animals required to produce 1 × 109 kg HCW beef. Three production treatments were compared, 1 representing average U.S. production (control), 1 with a 15% increase in ADG, and 1 with a 15% increase in finishing weight (FW). For each treatment, various socioeconomic scenarios were compared to account for uncertainty in producer and consumer behavior. Environmental impact metrics included feed consumption, land use, water use, greenhouse gas emissions (GHGe), and N and P excretion. Feed cost, animal purchase cost, animal sales revenue, and income over costs (IOVC) were used as metrics of economic viability. Willingness to pay (WTP) was used to identify improvements or reductions in social acceptability. When ADG improved, feedstuff consumption, land use, and water use decreased by 6.4%, 3.2%, and 12.3%, respectively, compared with the control. Carbon footprint decreased 11.7% and N and P excretion were reduced by 4% and 13.8%, respectively. When FW improved, decreases were seen in feedstuff consumption (12.1%), water use (9.2%). and land use (15.5%); total GHGe decreased 14.7%; and N and P excretion decreased by 10.1% and 17.2%, compared with the control. Changes in IOVC were dependent on socioeconomic scenario. When the ADG scenario was compared with the control, changes in sector profitability ranged from 51 to 117% (cow-calf), -38 to 157% (stocker), and 37 to 134% (feedlot). When improved FW was compared, changes in cow-calf profit ranged from 67% to 143%, stocker profit ranged from -41% to 155% and feedlot profit ranged from 37% to 136%. When WTP was based on marketing beef being more efficiently produced, WTP improved by 10%; thus, social acceptability increased. When marketing was based on production efficiency and consumer knowledge of growth-enhancing technology use, WTP decreased by 12%-leading to a decrease in social acceptability. Results demonstrated that improved efficiency also improved environmental impact, but impacts on economic viability and social acceptability are highly dependent on consumer and producer behavioral responses to efficiency improvements. [ABSTRACT FROM AUTHOR]

The objective of this study was to quantitatively summarize the literature describing endophyte-infected fescue effects on cattle ADG. The effects of three different infection-level measurement methods were tested using 138 treatments from 20 articles. The dataset was split into two subsets based on whether SEM were reported for the ADG measurements: only complete-SEM data (CSD) and all data including missing-SEM data (MSD). Weighting factors were calculated as 1/SEM in both datasets when SEM was reported. In the MSD group, values with missing SEM were weighted according to the average of the reported SEM. Three endophyte-infected fescue measurement methods were employed in the literature including: endophyte infection as a percentage of infected tillers (E%); ergovaline concentration in ppb ([E]); and total ergot alkaloid concentration in ppb ([TEA]). Three types of weather variables were used to explain climate differences: base measurements (temperature, humidity, and relative humidity), climate indices (heat index and temperature-heat index), and a novel parameter accounting for the average infection- level change based on date and duration of study (AEL). Models for ADG were derived in a 2x3x3 factorial approach using backwards stepwise elimination multiple regression to determine significant parameters. For each 100 ppb increase in [E] and [TEA], ADG decreased by 39 and 33 g/d, in both the CSD and MSD. For each 10% increase in E%, ADG decreased by 39 and 47 g/d in the CSD and MSD. All endophyte infection level relationships were significant (P<0.05) but no other significant variables were identified. Visual data inspection suggested an infection threshold (IT) was needed because intermediate measurements of infection-level were scarce. Significant ITs were identified at 60 ppb [E] and 11 E%, with no IT identified for [TEA] due to insufficient sample size. The ADG was 40 and 49% higher below the IT, for [E] and E% in the CSD. The use of an IT resulted in significant effects of climate variables in all three categories (P<0.05). Infection levels above the IT combined with increasing temperature, temperature-humidity index, or AEL resulted in ADG decreases greater than would be expected from infection level alone. The results of this meta-analysis show a significant negative relationship between endophyte-infection level and ADG in growing cattle. An IT for measuring the endophyte infection level increased accuracy of models and shows an additional negative relationship between various climate variables and ADG. [ABSTRACT FROM AUTHOR]

Basal metabolic rate (BMR), estimated by housing animals in metabolic chambers, measures total daily heat and gas production. The use of this practice in bovines has decreased because of practical and economic challenges, resulting in a limited understanding of factors affecting BMR. A recent technique developed by Renquist et al. used a fluorescence assay to measure BMR in zebrafish, which could be an economic and practical method to compare BMR in bovines. Our objective was to evaluate the repeatability, practicality, and sensitivity of this assay using muscle samples collected from heifers fed different combinations of soluble fiber and rumen degradable starch. Six yearling Holstein heifers were used in a partially replicated Latin Square experiment with 4 dietary treatments consisting of high and low dietary starch and fiber arranged factorially. Heifers underwent an 18 day diet adaptation period, after which a 300 mg muscle biopsy was collected from the semitendinosus muscle. Biopsies were immediately placed in a pre-test media for approximately 45 minutes during transport from the farm to the lab. Samples were then transferred to individual wells of a 96 well plate containing 360 uL of test solution media (30 mL DMEM, 7.5 mg fungizone, 0.12 mg chloramphenicol, 0.030 mg ampicillin, and 0.48 mL of AlamarBlue). Sample fluorescence was read at time 0 and every fifteen minutes over a two hour period with excitation at 530 nm and emission at 590 nm. Change in fluorescence was representative of relative basal metabolic rates of the individual tissue samples. Although the assay is time sensitive, it is feasible to prep all animals, collect biopsies within 15 minutes and allow the remaining 45 minutes for transport to the laboratory. Relative change in fluorescence was evaluated for the fixed effects of time and diet while accounting random effects of cow and period. The length of time a sample was left to fluoresce increased the signal strength but there was no interaction between fluorescence time and treatment (P>0.05). Ruminally degradable starch (P=0.01) and animal (P=0.001) significantly affected skeletal muscle BMR measured by fluorescence change. Accordingly, this fluorometric assay, is an economical, practical and sensitive test for detecting BMR differences among individual cattle and changes that arise as a result of diet. [ABSTRACT FROM AUTHOR]

Breeding and management of animals to achieve improved feed efficiency is a significant priority for the beef industry. Feed conversion ratio (FCR) and residual feed intake (RFI) have become popular measurements for feed efficiency, although both have limitations and practical challenges. The identification of additional, cost-effective indicators of feed efficiency is needed to improve breeding programs. We hypothesized that volatile fatty acids (VFAs), the end products of rumen microbial fermentation and the primary energy source for ruminants, could potentially dictate feed utilization for growth and production. In this study, we tested whether residual VFA (rVFAs) could serve as a predictor of feed efficiency. Rumen content was collected from a total of 204 beef (Angus, Charolais, and Kinsella composite) steers raised under a Growsafe® system, and VFA concentrations (mol/L) were analyzed by gas chromatography. Microbial populations were estimated using total copy numbers of 16S rRNA genes for bacteria and archaea using quantitative PCR (qPCR). Animal phenotypic measures including body weight (BW), dry matter intake (DMI), average daily gain (ADG), feeding frequency, RFI, and carcass performances were collected. The feed was collected at the time of rumen sample collection, and its nutrient content was analyzed. VFA concentrations and production rates were predicted using the Molly mathematical model for each animal based on observed BW, DMI, and ration composition. Residual VFA concentrations were calculated as observed minus predicted VFA concentration. The relationships among digestion parameters and rVFA were tested using stepwise, backward linear regression, which was also used to test rVFA as a predictor of feed efficiency. Residual acetate (ResAc), propionate (ResPro), and total VFA concentrations were significantly correlated with BW, DMI, and breed. Residual butyrate (ResBu) was correlated only with DMI. Total bacterial copy number was negatively correlated with eating frequency (P < 0.05) and ResAc (P < 0.01) and positively associated with ResPro (P < 0.01) concentrations. Total archeal copy number was inversely related to ResPro. RFI was significantly affected by DMI (P < 0.01) and ResAc and showed a significant negative relationship with ResPr and ResBu (P < 0.05). Similarly, FCR was significantly affected by DMI, ADG, and breed. Both ResPr and ResBu had non-significant (P < 0.1), inverse relationships with FCR. Although the work needs to be independently evaluated, our preliminary results identified the potential of using rVFA concentrations to predict feed efficiency traits in beef steers. [ABSTRACT FROM AUTHOR]

It has been demonstrated that Faecalibacterium prausnitzii (FP) has the capacity to produce anti-inflammatory products, including production of interleukin-10 (IL-10) an immunosuppressive factor that inhibits the synthesis and bioactivity of cytokines, and increases butyrate production. Administration of FP to dairy calves during the first week of life decreased incidence of diarrhea, improved ADG, and enhanced weaning weight. The objective of this study was to evaluate the effect of FP administration at birth on growth and performanceWinter- born calves from Virginia Tech's commercial and purebred beef cattle herds were enrolled in this study. Cows previously diagnosed as pregnant were stratified by breed, BW and parity, and their calves were randomly assigned to one of two treatments: 1) oral administration at birth of FP at a concentration of 1.34 x 10^7 CFU/mL (FPS; n = 54; 39 males and 15 females); or 2) a placebo oral administration at birth of culture media containing no bacteria (CTR; n = 57; 39 males and 18 females). At birth, individual calf BW, and sex were determined. Calves were maintained with their dams until weaning as a single group, and were monitored daily for incidence of diarrhea. BW was determined monthly until weaning. The MIXED procedure of SAS was used to analyze all data, the statistical model included the fixed effects of treatment and breed, and random effects of calf sex, cow BW and parity as well as all interactions. Calf birth BW was similar (P = 0.830) between treatments (80.6 ± 1.6 kg and 81.1 ± 1.75 kg for CTR and FPS, respectively), male calves were heavier (P = 0.006) at birth compared to females, but no treatment × sex interaction was detected (P = 0.45). No calves were treated for diarrhea during the experiment. Calf ADG was similar (P = 0.34) between treatments (1.09 ± 0.02 kg and 1.13 ± 0.03 kg for CTR and FPS, respectively). However, adjusted weaning weight for 205 d tended (P = 0.08) to be greater for FPS calves (275.6 ± 3.6 kg) compared to CTR calves (268.9 ± 4.0 kg). Our results indicate that FP has the potential to improve beef calf pre-weaning performance, however further investigation is warranted. [ABSTRACT FROM AUTHOR]

Reproductive efficiency is a key component of sustainable dairy production, significantly influencing herd profitability. Because of the known interactions between energy status, insulin sensitivity, and the hypothalamus- pituitary-gonadal axis, volatile fatty acid dynamics are likely to influence reproductive status via downstream signaling. Altering volatile fatty acid dynamics has been minimally explored in relation to reproductive status and could be a viable strategy for improvements in this area. The objective of this study was to investigate the effect of increased propionate status on progesterone profiles in dairy heifers. Eleven Holstein heifers, 8 to 10 months of age and 550 to 800 lb, were subject to an OvSynch + CIDR procedure, then assigned to two treatments and given a continuous IV infusion of either sodium propionate (PRO; 61.6 mmol/hr; n=5) or saline (CON; n=6) at a matching infusion volume for 5 days. Daily blood samples were taken from animals for an additional 7 days after the end of the infusion. Plasma propionate concentrations increased over the first 9 hours in PRO cows. Between hour 9 and day 3, plasma propionate concentrations decreased in the PRO group until they matched levels seen in CON cows. No difference in plasma propionate concentrations were identified after day 3. There were no differences in daily plasma acetate or beta-hydroxybutyrate levels seen between treatments for any timepoints within the experimental period (P > 0.10). Plasma progesterone levels rose at a similar rate in both PRO and CON cows, however, PRO cows had the tendency to reach greater maximum progesterone levels (4.19 vs 3.73 ng/mL; P = 0.087). The results of this study indicate that although infusing propionate to dairy heifers initially increases plasma propionate levels, there appears to be a metabolic shift allowing the animal to clear the surplus propionate and return plasma concentrations to basal levels. This phenomenon warrants further investigation because it suggests ample capacity of the animal to metabolize propionate, provided ruminal fermentation can be manipulated to deliver additional quantities to the bloodstream. Further, the increased magnitude of progesterone response suggests a role for propionate, and volatile fatty acid supply and subsequent metabolism, in modulating reproductive performance. [ABSTRACT FROM AUTHOR]

In ruminants, starch is acknowledged as glucogenic, and fiber as acetogenic. Although these impacts of dietary nutrient concentrations are well characterized, effects of ruminal nutrient degradability on blood metabolites are poorly understood. The focus of this study was to evaluate the effects of degradable fiber and starch supplies on blood volatile fatty acid (VFA), glucose, and beta-hydroxybutyrate (BHB) concentrations. Six Holstein heifers (BW 725 ± 25 lb) were used in a partially replicated Latin Square experiment with 4 treatments (low or high ruminally degradable fiber and starch arranged factorially). During each period, animals were adapted to treatment diet for 17 days, and on day 18 blood samples were collected by coccygeal venipuncture. Blood samples were centrifuged for 15 minutes immediately after collection to isolate plasma, and were preserved in 4oC. Blood glucose and BHB were quantified using colorimetric assay kits, and blood VFA concentrations were determined via GCMS. Data were analyzed using a mixed model with ruminally degradable fiber and starch as fixed effects and cow and period as random effects. The interaction between degradable fiber and starch concentrations were also tested. Blood acetate (P>0.10), propionate (P>0.10), and glucose (P>0.10) were not influenced by starch, fiber, or the starch by fiber interaction (P>0.10). The lack of a significant change in blood acetate and propionate was unexpected given that shifts in fermentation patterns, and subsequently, shifts in blood VFA concentrations were anticipated. Although BHB was not affected by starch or the starch by fiber interaction (P>0.10), dietary supply of degradable fiber (P=0.002) increased blood BHB concentrations. The significant relationship between dietary degradable fiber supplies and blood BHB concentrations suggests enhanced fermentation of fiber in the rumen contributes to blood BHB concentrations. Blood BHB is influenced by the breakdown of free fatty acids in the liver, or by increased ruminal butyrate production. Given that these diets were in excess of the animal's energy requirements and had similar fatty acid content, it is unlikely that the elevated BHB is indicative of liver ketogenesis, rather, we hypothesize that the elevated BHB was caused by increased butyrate absorption from the rumen. Additional work is needed to understand how and why soluble fiber contributes to butyrate production and absorption rates. [ABSTRACT FROM AUTHOR]

Endophyte-infected tall fescue occupies most grazing lands in the Southeastern U.S. and is associated with poor growth and reproductive performance. Supplementing bicarbonate to cattle grazing endophyte-infected tall fescue was hypothesized to be a strategy to alleviate these negative performance outcomes. The objective of this study was to evaluate growth and reproductive characteristics of heifers consuming endophyte-infected tall fescue with or without sodium bicarbonate supplementation. Forty-eight heifers (8 mo; BW = 589 ± 53 kg) were blocked by BW and assigned to pens and treatments. Heifers were group-housed and fed individually using Calan gates. Treatments were arranged as a 2 × 2 factorial design with heifers receiving either high- or low-endophyte fescue seed with (E+B, E-B) or without (E+, E-) sodium bicarbonate supplementation. Heifers were fed a corn silage diet; seed and bicarbonate were supplemented at 1.5 kg/day and 0.25 kg/day, respectively. Heifer BW was recorded on sequential days at the start and end of the 84 d experiment and every 14 d. Feed intake and refusals were collected daily. The BW and DMI data were used to estimate ADG and G:F. Reproductive tract scores (RTS) were performed every 28 d via transrectal palpation and ultrasonography. Results were analyzed after the 2nd ultrasound (56 d) and at the end of the experiment. At d 56, RTS (P = 0.005) was affected by the interaction of bicarbonate supplementation and fescue seed type, and G:F (P = 0.061) and ADG (P = 0.058) tended to be affected. In general, RTS, G:F, and ADG of all other treatments were improved compared with the E+ treatment. Neither factor affected DMI at d 56 (P > 0.10). By d 84, bicarbonate supplementation tended to decrease ADG (P = 0.051) and decreased G:F (P = 0.016), and infected fescue consumption tended to decrease DMI (P = 0.060). On d 56, bicarbonate showed promise as a strategy to ameliorate the negative effects of endophyte-infected fescue consumption; however, by the end of the study, no effects of fescue seed type on ADG or G:F were observed. Short-term bicarbonate supplementation appears to be a promising strategy to eliminate negative production responses associated with endophyte-infected fescue consumption; however, additional research is needed to fully understand why this benefit was not sustained over the full experimental period and how the strategy would translate to traditional pasture systems where animals can self-select a bicarbonate supplementation level. [ABSTRACT FROM AUTHOR]

This study estimated new and variable individual AA efficiencies that could be incorporated into diet formulation for lactating sows. Literature used to estimate AA efficiencies in the NRC (2012) swine model were mined for feed intake, sow weight loss, dietary N, litter weight gain, litter size, milk yield, and milk AA composition data. Models were derived to estimate variable AA use efficiencies in milk. A mixed-effect regression of AA efficiencies on diet composition, feed intake, and weight loss was conducted accounting a random study effect. Models were evaluated using the root mean squared error (RMSE), concordance correlation coefficient (CCC), and corrected Akaike information criteria. Arginine, Lys, Phe, Thr, and Val efficiencies decreased (P < 0.05) with increasing dietary N and all AA efficiencies increased (P < 0.05) with increasing milk yield. Only Leu and Met efficiencies decreased (P < 0.05) with increasing weight loss. Equations predicted measured AA efficiencies with RMSE between 5.3 and 15.4% and CCC between 0.97 and 0.99. The AA efficiencies were also modeled as a function of dietary N, feed intake, weight loss, and efficiencies of Leu, Met, and Cys (these explanatory AA were selected based on their individual fit for direct prediction). Histidine, He, and Lys efficiency models improved with Leu and Cys efficiencies included as covariates but models of Arg, Phe, Thr, or Val efficiency did not improve. Energy allowable milk was calculated based on the difference between energy supply and maintenance requirements and the lactation energy use efficiency. Amino acid allowable milk was calculated from modeled AA efficiencies and standardized ileal digestible (SID) AA supply. The minimum of energy and AA allowable milk estimates and their mean were calculated. A first-limiting nutrient model (minimum of energy and AA allowable milk) had an RMSE of 110%. A co-limiting nutrient model (mean of energy and AA allowable milk) had a lower (32%) RMSE. To more fully investigate the utility of a co-limiting nutrient model, a multisubstrate Michaelis-Men-ten equation was fit to predict milk yield as a function of AA and ME supply. After a stepwise elimination of nonsignificant parameters, the final model (based on Arg, Leu, Met, Phe, Thr, and Val SID intake) returned a RMSE of 10% and very good concordance (0.77). These results suggest that nutrients co-limit milk production and that moving toward a more response-driven model may help define more precise diets that account for dynamic mammary uptake of AA. [ABSTRACT FROM AUTHOR]