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Enteric methane (CH4) is produced during the anaerobic fermentation of organic matter and represents an energy loss for ruminants. Diet and animal characteristics mainly determine CH4 emissions. However, there is limited information regarding the relationship between feeding behavior and CH4 emissions in growing steers consuming different diets. This experiment aimed to evaluate the feeding behavior of growing steers with divergent residual methane emissions (RCH4) during the backgrounding and finishing phases. Two hypotheses were evaluated: 1) the steers would not change the initial RCH4 classification when moving from backgrounding to finishing phases, and 2) steers with divergent RCH4 would show different feeding behavior. Angus steers (n = 60) were placed in two pens and were classified as high, medium, and low RCH4 during both phases. During the backgrounding phase, steers [209 ± 26 kg of initial body weight (BW)] were fed a total mixed ratio (TMR) with 46% neutral detergent fiber (NDF) and 0.86 Mcal/kg DM of net energy of gain (NEg) for 60 d. During the finishing phase, steers (517 ± 40 kg of initial BW) were fed a TMR with 16.8% NDF and 1.37 Mcal/kg DM of NEg for 80 d. Feed intake and gas flux were determined daily using Smartfeed and Greenfeed technology. Steers were weighed every 2 wk during each phase to determine average daily gain (ADG). The number of meals (NM), meal size (MS), time per meal (TM), intervals between meals (IM), and intake rate (IR) were calculated using 5 min as a meal criterion. Individual RCH4 classification rank during the backgrounding and finishing phases was analyzed using a chi-square test. Feeding behavior was analyzed using a mixed model with RCH4 classification and animal as fixed and random effects, respectively. No relation (P = 0.5) existed between individual RCH4 classification during the backgrounding and the subsequent RCH4 classification during the finishing phase. In either phase, feed intake or ADG was not different (P > 0.05) among divergent RCH4 groups. Feeding behavior was not different (P > 0.05) among RCH4 groups during the backgrounding phase, but MS and TM were greater (P < 0.05) in steers with high RCH4 during the finishing phase. Steers classified as low RCH4 showed less CO2 and CH4 production and less O2 consumption than medium and high RCH4 in either phase. In conclusion, growing steers were re-ranked according to the RCH4 classification during the backgrounding and finishing phases. Animal performance was not related to RCH4 classification. However, steers with decreased RCH4 showed less MS during the finishing phase. Also, CO2 and CH4 were less in low RCH4 steers during both phases. Further work should be conducted to recognize differences in fermentation and metabolism of lower RCH4 steers for developing selection and management interventions. [ABSTRACT FROM AUTHOR]

Across the Western U.S., beef cattle spend considerable time grazing extensive rangelands. Enteric methane (CH4 ) production in grazing systems represents more than 80% of the total enteric CH4 emissions. However, more measured CH4 data from cattle grazing extensive rangelands is needed to inform measurement, reporting, modeled emissions, and to identify mitigation opportunities. The availability of pasture-ready automatic head-chamber systems (AHCS; C-Lock Inc, Rapid City, South Dakota) has allowed the determination of emissions in rangelands. In this regard, different methods to ensure an accurate determination of enteric CH4 using this measurement technique have been evaluated in recent years. An initial step to obtaining accurate enteric emissions data is ensuring efforts secure adequate AHCS visitation. Investigations in small (< 99 ac) pastures have shown that ≥ 15 visits to ≥ 55 visits in feedlot pens are adequate for robust enteric CH4 production data. Here, our goal is to examine AHCS visitation outcomes to inform the use of this technique in extensive rangeland. For two grazing seasons at the USDA ARS Central Plains Experimental Range (CPER), we have studied enteric CH4 emissions from yearling steer herds ranging in size from 26 to 60 animals in continuously stocked rangeland (Table 1). After 30 d of acclimation in 2022, 46% of individuals continued using an AHCS until the end of the drought-shortened grazing season, totaling 60 d of constant AHCS exposure. In 2023, individuals were measured first at post-weaning, and those with ≥ 15 visits to an AHCS were stocked at CPER. These steers were previously exposed to an AHCS on average 69 d earlier (range: 28 to 118). Of these 60 individuals, 68% used the two available AHCS ≥ 15 times when grazing rangeland for 76 d, totaling 137 d of discontinuous AHCS exposure. While grazing, individual visits per season were reduced in 2022 and substantially greater in 2023. At this point in our enteric CH4 emission investigation, we learned that either exposing an individual multiple times to an AHCS after weaning or doubling the days of exposure in the acclimation phase increases visitation during the measurement phase by about 20% at the herd level and 450% on an individual basis. Insights learned on rangeland have uncovered several considerations for measuring enteric CH4 emissions in extensive environments: lengthy past exposure to AHCS is ideal for adequate visitation during the measurement phase and visitation of unacclimated individuals is unlikely during the measurement phase. Further work should determine the true number of individual visits required for accurate methane measurement in extensive rangelands and evaluate 1) efficacy of different acclimation practices, 2) continued use of previously exposed animals and temporal visitation decay, and 3) alternative placement of AHCS, and use of palatable attractants to increase AHCS visitation may improve measurement of enteric CH4 emissions. [ABSTRACT FROM AUTHOR]

The objective of the current study was to investigate the effects of supplemental rumen-protected lysine and methionine (SMART) and ractopaminehydrochloride (RAC) on cattle growth performance and carcass characteristics of finishing calf-fed Holstein steers. Calf-fed Holstein steer calves [n = 96; body weight (BW) = 466 ± 29 kg] were used to evaluate the interaction of ractopamine and supplemental methionine and lysine on growth performance and carcass characteristics. Steers were blocked by initial off-truck BW and assigned within BW grouping to 16 pens (6 steers/pen). From d 1 to 67, all steers received the basal steam-flaked corn-based finishing diet. From d 68 to harvest (d 103), steers received experimental diets consisting of two levels of RAC (0 vs. 300 mg/hd/d; Optaflexx, Elanco US, Inc., Greenfield, IN) and two levels of supplemental SMART (0 vs. 0.67% DM basis, Smartamine ML Adisseo, Alpharetta, GA). There was an interaction (P = 0.04) between RAC and SMART supplementation, where cattle fed the combination of both supplements had an increase in dry matter intake (DMI) compared with cattle fed either RAC or SMART. However, there was no interaction (P ≥ 0.17) of treatments in other growth performance or carcass characteristic variables evaluated in the study. Carcass adjusted average daily gain (ADG) and energy efficiency of the diet increased (P ≤ 0.02) on cattle supplemented with SMART. Moreover, carcass-adjusted final BW and feed efficiency, as well as energy efficiency, increased (P ≤ 0.05) on cattle supplemented with RAC. However, neither SMART nor RAC supplementation affected (P ≥ 0.13) cattle DMI. Both SMART and RAC supplementation increased (P ≤ 0.03) carcass weight, with no effect (P ≥ 0.17) in other carcass characteristics. In conclusion, both SMART and RAC supplementation enhances cattle growth performance with no detrimental effects on carcass characteristics of calf-fed Holstein steers. [ABSTRACT FROM AUTHOR]

One hundred sixty-eight Holstein steer calves (133.4 ± 7.9 kg) were used to evaluate the influence of virginiamycin (VM) supplementation on cattle growth performance and liver abscess incidence, and the effect of feeding 100% vs. 87% of metabolizable protein (MP) requirements during the initial 112 d on growth performance, efficiency of energy utilization, and carcass characteristics. Steers were balanced by weight and assigned to 28 pens (6 steers/pen). During the initial 112-d feeding period, dietary treatments consisted of two levels of MP (100% vs. 87% of expected requirements) supplemented with or without 22.5 mg/kg VM in a 2 × 2 factorial arrangement. There were no VM × MP supplementation interactions (P  ≥ 0.14) on any of the parameters measured in both experiments. Calf-fed Holstein steers supplemented with VM increased (P  ≤ 0.03) overall average daily gain (ADG), feed efficiency (G:F), observed/expected net energy (NE) values for maintenance and gain, and final body weight (BW). Cattle fed VM also increased (P  ≤ 0.04) carcass weight, dressing percent, and longissimus muscle area. However, there was no effect (P  ≥ 0.22) of VM supplementation on any other carcass characteristics. Calf-fed Holstein steers fed 100% MP requirements during the initial 112-d feeding period had greater (P  ≤ 0.02) ADG, G:F, observed/expected NE values for maintenance and gain, and live BW compared with steers fed 87% of the expected MP requirements. However, there was no effect (P  ≥ 0.17) of MP supply during the initial 112-d period on overall (342 d) growth performance measurements. The incidence of liver abscesses was low (averaging 7.7%) and not affected by dietary treatments. We conclude that, independent of MP supplies, supplemental VM enhances overall growth performance and efficiency of energy utilization of calf-fed Holstein steers. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the relationship between pulmonary arterial pressure (PAP) expected progeny differences (EPD) and methane emissions. Pulmonary arterial pressure is an indicator of pulmonary arterial hypertension in cattle and is especially relevant at high altitudes, with increasing importance in moderate elevation feedlot and finishing systems. Enteric methane emissions from cattle are increasingly emphasized due to their contribution of greenhouse gases in the agricultural sector. As pulmonary arterial hypertension continues to be an issue in high altitudes and feedlots, understanding relationships with methane emission rates will be useful for both concomitant selection with the goal of improving environmental sustainability. The PAP EPD data were collected on 123 total heifers (n = 37) and steers (n = 86) located on a ranch in southern Wyoming at an elevation of 2,194.56 meters. Gas emissions were collected using a GreenFeed system (C-Lock, Rapid City, South Dakota), which measures the gas fluxes of individual animals at the CSU ARDEC facility at an elevation of 1,557.53 meters. Individual animal methane emissions were measured as grams/day. A generalized linear regression model was used to regress average daily methane emissions (mean = 163.08, SD = 38.74, min = 87.72, max = 247.03) on PAP EPD (mean = -0.464, SD = 1.565, min = -6.382, max = 4.286), pen, and age in days (mean = 258.2, SD = 20.009, min = 200, max = 298). The PAP EPD (P = 0.484) did not account for a significant amount of variation in methane emissions. Additionally, the effect of pen (P < 0.05) and age (P < 0.05) were significant sources of variation for methane production. The effects of pen had a range of 60.916 units of methane emission/day (P < 0.05). Age of the individual was evaluated as a linear covariate and had a solution of 0.678 units of methane emission/day (P < 0.05), suggesting that older individuals had increased methane emissions. These results show no statistical relationship between PAP EPD and methane in these data. While preliminary results suggest that selection for low PAP EPD individuals will have no adverse effects on sustainability metrics, future research is needed to fully understand the relationship between beef cattle production traits and sustainability metrics. [ABSTRACT FROM AUTHOR]

Objectives were to compare in vitro and in situ disappearance of dry matter (DM), neutral detergent fiber (NDF), and starch of traditional (unprocessed and rolled) and hulless (unprocessed) barley. Experiment 1: three barley sources were compared using in vitro techniques. The sources were: 1) traditional barley that was not processed, 2) traditional barley processed through a roller mill, and 3) hulless barley that was not processed. For in vitro incubation, each barley source was ground through a 1-mm screen. Ground barley sources were weighed into bags (25 micron porosity) and incubated in ruminal fluid from two steers fed 80% rolled corn for 3, 6, 12, 24, 48, or 72 h. Intact bags were assayed for NDF; remaining bags were opened and the residual was removed and analyzed to determine disappearance of DM and starch. Experiment 2: the barley sources used in Exp. 1 were compared using in situ techniques. For in situ analysis, each barley source was ground in a Wiley mill with no screen to mimic mastication. Artificially masticated samples were weighed into Dacron bags (50 ± 10 micron porosity) and incubated in eight ruminally fistulated steers (n = 8) for 3, 6, 12, 24, 48, and 72 h. Residual contents were analyzed to determine in situ disappearance of DM, NDF, and starch. Data were analyzed using the MIXED procedures of SAS (9.4 SAS Institute, Cary, NC) with repeated measures. DM disappearance was greatest (P < 0.05) for hulless barley in vitro and for rolled barley in situ, regardless of time postincubation. For both trials, NDF disappearance was greatest (P < 0.05) for hulless barley, regardless of time postincubation. Starch disappearance at all time points was greatest (P < 0.05) for rolled barley in situ. Starch disappearance was greater (P < 0.05) for hulless barley at 6 h of in vitro incubation compared to rolled and unprocessed barley, whereas starch disappearance in vitro was comparable (P = 0.60) between barley sources. When the grains were compared in vitro, minor differences were noted, presumably because barley sources were finely ground prior to incubation. Compared to in vitro estimates, in situ techniques had greater variation in ruminal degradation estimates. Differences observed between in situ and in vitro techniques are driven largely by differences between the procedures. Although laboratory methods are widely used to estimate ruminal degradation, these techniques did not provide comparable estimates of ruminal degradation of barley. [ABSTRACT FROM AUTHOR]

Objective of the current study was to evaluate the effects of tannin supplementation on cattle growth performance, energetic efficiency, and carcass characteristics of calf-fed steers. One hundred and sixty dairy steer calves with initial body weight (IBW) of 129.85 ± 3 kg, were blocked by IBW and randomly assigned to 40 pens (4 steers/pen; 10 pens per dietary treatment). Dietary treatments were: 1) Control (no additives); 2) MON (30 mg/kg monensin); 3) TAN (15 g/kg ByPRO; 70% condensed tannin; Silvateam USA, Tontitown, AR); and 4) MON+TAN (30 mg/kg monensin + 15 g/kg ByPRO). All steers were fed a similar steam-flaked corn-based diet (63.5% steam-flaked corn, 12.0% hay, 17.5% of dry distillers grains with solubles, 4.0% cane molasses, and 3.0% vitamin/mineral supplement). All cattle were slaughtered after 328 days of feed. There were no effects (P = 0.13) of dietary treatment on final BW (615 ± 22 kg), overall average daily gain (1.48 ± 0.07 kg/day), overall dry matter intake (7.93 ± 0.39 kg/day), overall gain to feed ratio (0.187 ± 0.07), and overall observed vs. expected net energy for maintenance and gain (1.00 ± 0.03 and 1.00 ± 0.04, respectively). However, cattle receiving MON or MON+TAN supplementation increased (P = 0.04) BW and gain to feed ratio in the first 112 days on feed compared with cattle in the control treatment. Moreover, cattle in the 2 dietary treatments receiving monensin supplementation tended (P = 0.09) to increase average daily gain and gain to feed ratio on the first 112 days on feed compared with cattle in the control treatment. There were no effects (P = 0.22) of feed additive supplementation on hot carcass weight (380.7 ± 14.7 kg), dressing percentage (61.83 ± 1.05%), kidney, pelvic, and heart fat (3.32 ± 0.19%), backfat thickness (0.73 ± 0.12 cm), longissimus muscle area (83 ± 4.83 cm2), marbling score (494 ± 48), and calculated yield grade (2.94 ± 0.24). Moreover, there were no effects (P = 0.55) of dietary treatment on percent of liver abscess incidence, regardless of diet, calf-fed steers in the current study had 3.75% of liver with abscess. [ABSTRACT FROM AUTHOR]

Objective of the current study was to evaluate the effects of cattle breed (Holstein vs Angus × Holstein) on growth performance, energetic efficiency, and carcass characteristics of calf-fed steers. Eighty Holstein (HOL), initial body weight (IBW) of 128.7 ± 3 kg, and 80 Angus × Holstein cross (CROS) with IBW of 127.1 ± 3 kg, were blocked by IBW and randomly assigned to 40 pens (4 steers/pen; 20 pens per breed). All steers were fed a similar steam-flaked corn-based diet (63.5% steam-flaked corn, 12.0% hay, 17.5% of dry distillers grains with solubles, 4.0% cane molasses, and 3.0% vitamin/mineral supplement). All cattle were slaughtered after 328 days of feeding. There was no effect (P = 0.13) of cattle breed on final body weight (615 ± 22 kg) and overall average daily gain (1.48 ± 0.07 kg/day). However, calf-fed HOL steers had greater (P = 0.04) overall dry matter intake compared with calf-fed CROS steers (8.06 vs. 7.79 ± 0.39 kg/day; respectively). Therefore, calf fed CROS steers had greater (P = 0.01) grain to feed ratio compared with calf-fed HOL steers (0.192 vs. 0.182 ± 0.005; respectively). Moreover, calffed CROS steers had greater (P < 0.01) utilization of dietary net energy for maintenance (2.29 vs. 2.29 ± 0.06 Mcal/kg; respectively) and gain (1.51 vs 1.61 ± 0.06 Mcal/kg; respectively) compared with calf-fed HOL steers. Calf-fed CROS steers had greater (P = 0.02) hot carcass weight (HCW; 386.3 vs. 375.2 ± 14.7 kg; respectively), dressing percentage (DP; 62.3 vs. 61.4 ± 1.05%; respectively), longissimus muscle area (LMA; 86.9 vs. 79.1 ± 4.83 cm2; respectively), backfat thickness (0.89 vs. 0.55 ± 0.12; respectively), and marbling score (538 vs. 449 ± 48; respectively). However, there was no effect (P = 0.26) of cattle breed on calculated USDA yield grade (2.94 ± 0.24). Moreover, there was no effect (P = 0.39) of cattle breed on incidence of liver abscesses. Therefore, cross breeding calf-fed Angus × Holstein increased HCW, DP, LMA, and marbling compared with purebred calf-fed Holstein steers. Moreover, regardless of cattle breed, calf-fed steers in the current study had only 3.75% of liver with abscess. [ABSTRACT FROM AUTHOR]

Enteric methane emissions from cattle are the largest source of agricultural methane emissions; however, measuring enteric methane emissions is costly and infeasible in many environments. Consequently, prediction of enteric methane emissions for greenhouse gas emissions inventories for reporting and carbon market purposes is an important alternative to measurement. The objective of the current experiment was to evaluate the relationship between feed intake and methane emissions, and to compare observed methane emissions with commonly used enteric methane emissions prediction equations. Cattle (n = 194; steers n = 99, heifers n = 58, bulls n = 37) were housed at the Colorado State University Climate Smart Research pens equipped with Smartfeed feed intake measurement and Greenfeed emissions monitoring systems (C-Lock, Rapid City, SD). Body weight, body weight gain, dry matter intake, and methane emissions were collected for 37 days for each individual animal. All summary statistics and univariate fit analyses were conducted in JMP Pro 15.0 (SAS Institute Inc. Cary, NC). Observed methane emissions were compared with three extant methane prediction equations: IPCC tier 2 (IPCC), Moraes et al. (2014) animal-level (MAL), and Mills et al. (2003) non-linear equation 2 (MNL). Mean observed methane emissions were 185.3 g· animal-1· day-1 [standard deviation (SD) = 31.1], 135.6 g· animal-1· day-1 (SD = 29.3), and 177.8 g· animal-1· day-1 (SD = 20.1), for steers, heifers, and bulls, respectively. Across all 194 animals mean feed intake was 6.33 kg/d (SD = 1.65) and mean methane emissions were 169 g· animal-1· day-1 (SD = 36.2; Pearson correlation coefficient r = 0.65). When comparing observed vs. predicted methane emissions, MNL over predicted methane emissions (mean = 182.7 g· animal-1· day-1), whereas MAL (mean 119.3 g· animal-1· day-1) and IPCC (mean = 136.6 g· animal-1· day-1) underpredicted methane emissions (P < 0.01). Of the 3 prediction equations, MAL had the lowest root mean square error (RMSE) of 20.9 (R square = 0.50), followed by IPCC (RMSE = 27.2, R square = 0.42), and MNL (RMSE = 32.8, R square = 0.42). The current preliminary data suggests further refinement of enteric methane emissions prediction equations could improve inventories and estimates of enteric methane emissions on commercial cattle operations. [ABSTRACT FROM AUTHOR]

The dairy and beef industries have been identified as an important producer of methane emissions, yet little is known of its relationship to other economically relevant traits. Stayability (STAY) is a fertility and longevity-related trait with EPD (Expected Progeny Differences) representing predicted genetic differences in the probability of daughters remaining in the breeding herd until six years of age. Understanding the relationship between methane emissions and STAY might inform breeders of the consequences of selection on either trait. The objective of this study was to determine the relationship of methane emissions with STAY in Angus cattle (Bos Taurus) from Colorado State University's John E. Rouse Beef Improvement Center located in southern Wyoming. A total of 123 animals (86 steers, 37 heifers) were sorted into four different pens where individual methane emissions were measured using a GreenFeed system (C-Lock, Rapid City, South Dakota). Stayability was evaluated using EPD values. A general linear model was used to calculate the regression of the average methane emission of each animal measured in grams/day (mean = 163.08, SD = 38.75, min = 87.72, max = 247.03) on STAY (mean = 0.59, SD = 0.69, min = -2.41, max = 2.36), including age in days (mean = 258.2, SD = 20.01, min = 200, max = 298) and pen as effects in the model. The regression of methane emission on STAY EPD was 0.52, however, it was not significant (P = 0.87). The effect of pen was significant (P < 0.001?). Age was significant, having an effect of 0.6794 (P = 3.93e-08). This suggests that younger individuals had decreased methane emissions. These preliminary results indicate that there is no significant relationship between methane emissions and STAY EPD. [ABSTRACT FROM AUTHOR]

Adequate transfer of passive immunity (TPI) is a cornerstone for a proper health status of calves. In the literature, there is limited information on the prevalence of failure of TPI in dairy-beef crossbred calves and its effect on morbidity, mortality, and ADG during the preweaning period. Therefore, this study aimed to evaluate the association between TPI with morbidity, mortality, and ADG in preweaning dairy-beef crossbred calves. A total of 1,055 newborn dairy-beef crossbred calves were enrolled upon arrival at a calf-raising facility in California from January to August 2021. Farm of origin, genetic breed group, sex, and BW were recorded upon arrival. Blood was collected at 24 ± 1 h after arrival to evaluate serum IgG concentration, serum total protein (TP), and packed cell volume. Morbidity (diarrhea and respiratory treatment records) and mortality were recorded daily until 60 d of life. Calves were grouped into 2 genetic breed groups: Holstein × Beef (Ho × Be, 49.6%) and Jersey × Beef crossbred calves (Je × Be, 50.4%). Descriptive statistics and Cox proportional hazard models were created to evaluate the association of TPI categories for serum IgG (TPI-IgG: poor: <10.0 g/L, fair: 10.0-17.9 g/L, good: 18.0-24.9 g/L, and excellent: ≥25.0 g/L) and TP (TPI-TP: poor: <5.1 g/dL, fair: 5.1-5.7 g/dL, good: 5.8-6.1 g/dL, and excellent: ≥6.2 g/dL), sex, and genetic breed group with morbidity and mortality. Additionally, a mixed linear regression was performed to evaluate the association of sex, genetic breed group, and TPI categories with ADG. Overall morbidity and mortality were 84.8% (n = 895) and 2.5% (n = 26). Calves classified as TPI-IgG excellent were associated with the lowest (43.2% less) hazard of being treated compared with TPI-IgG poor calves. For mortality, dairy-beef crossbred calves with TPI-IgG excellent were associated with a reduction of 82.0% in the hazard of dying compared with TPI-IgG poor. The TPI-IgG poor and TPI-IgG fair calves were associated with a decreased ADG of 101.0 and 98.8 g/d, respectively, in comparison with TPI-IgG good calves. Average daily gain of TPI-IgG good and TPI-IgG excellent calves were not different. In our study, dairy-beef crossbred calves enrolled may have endured challenging conditions that increased morbidity. This reinforces the importance of high IgG levels to decrease morbidity and mortality and maximize ADG in dairy-beef crossbred calves raising systems. Further research should evaluate the long-term effects of TPI categories on the health and performance of dairy-beef crossbred calves., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Ruminants produce one-third of the anthropogenic methane ( CH 4 ) emissions worldwide, and 47% of the CH 4 emissions result from ruminants under grazing conditions. However, there is limited information regarding the appropriate number of visits to accurately determine enteric CH 4 emissions using the automated head-chamber system ( AHCS ) from growing beef cattle under intensive grazing conditions. Data from one experiment were analyzed to determine the number of visits to assess gas flux (CH 4 , carbon dioxide [ CO 2 ], and oxygen [ O 2 ]) from Angus-crossbreed steers grazing in a pivot-irrigated improved pasture. A total of 110 steers (324 ± 37.3 kg initial body weight) were selected and divided into two blocks. Steers were under intensive grazing management for 84 d. Depending on forage availability, steers were rotated at 2- to 4-d intervals. Pastures were predominately composed of cool-season forages. Two different databases using the same animals ( n  = 16) were defined to calculate the gas flux using the first 100 visits to an AHCS with 2 or more or 3 or more minutes of visitation length. The mean gas flux was estimated as the average for increasing (forward) or decreasing (reverse) the gas flux of 5-visit intervals starting with the first or the last 5 visits and increasing or decreasing until the full 100-visit dataset was utilized, respectively. Spearman and Pearson correlations were computed between the maximum visits and each shortened visit interval. Concurrently, the residual variance and the residual variance change were determined for each interval by fitting a mixed model. The minimum number of visits was defined when correlations with the total visits were greater than 0.95, and the residual variance was stabilized. The results indicated that the minimum number of visits needed to determine CH 4 production varied between 45 and 70, while CO 2 production and O 2 consumption varied between 45 and 50 according to the visitation length. Additionally, steers that visited the AHCS for 2 or more minutes in visit duration required a greater number of visits than those that visited for 3 or more minutes. Thus, based on the average daily visitation in this experiment (1.4 visit/d), the assessment of CH 4 emissions requires 32 d, while CO 2 production and O 2 consumption require between 32 and 36 d using 3 or more minutes of visit length from growing steers under intensive grazing conditions., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

The primary objective of this experiment was to evaluate the effects of a growth-hormone implant (Revalor-G, Merck Animal Health., Rahway, NJ, USA) and tannin supplementation (Silvafeed BX, Silva Team, San Michele Mondovi CN, Italy) on enteric methane (CH 4 ) emissions and estimated nitrogen (N) excretion in grazing steers. Steers ( n  = 20; initial body weight [IBW] = 343 ± 14 kg) were acclimated to use a portable automated head-chamber system (AHCS) to measure CH 4 and a SmartFeed Pro automated feeder for dietary supplementation (C-Lock Inc., Rapid City, SD, USA). After the training period, steers were randomly assigned to a 2 × 2 factorial arrangements of treatments, with 2 levels of growth-hormone implants, no-implant (NO-IMP) or implanted (IMP), and 2 levels of tannin supplementation, no tannin supplementation (NO-TAN) or tannin supplementation (TAN). This created 4 treatment groups: (1) NO-TAN and NO-IMP, (2) TAN and NO-IMP, (3) IMP and NO-TAN, and (4) TAN and IMP. Tannin was offered daily at 0.30% dry matter intake (DMI) through 0.5 kg/hd/d sweetfeed supplement (Sweetfeed Mix, AgFinity., Eaton, CO, USA) with a targeted tannin intake at 48 g/hd/d. No ( P  ≥ 0.05) implant × tannin interaction was detected for any dependent variable, so only the main effects of implant (NO-IMP vs. IMP) and tannin supplementation (NO-TAN vs. TAN) are discussed. Implant status did not affect ( P  ≥ 0.56) final body weight (FBW) or average daily gain (ADG) during the 90 d grazing period. There was no effect ( P  ≥ 0.15) of growth implant on CH 4 production or emission intensity (EI; g CH 4 /kg gain). Additionally, IMP steers tended ( P  ≤ 0.08) to have less CH 4 yield (MY; g CH 4 /g DMI) and higher blood urea nitrogen (BUN) than NO-IMP steers. Tannin supplementation did not impact ( P  ≥ 0.26) FBW or ADG. However, NO-TAN steers tended ( P  = 0.06) to have a greater total DMI than steers supplemented with tannin. No effect ( P  ≥ 0.22) of tannin supplementation was observed for CH 4 production and EI. Nitrogen utilization as measured through BUN, urine N, fecal N, or fecal P was similar ( P  ≥ 0.12) between TAN and NO-TAN animals. The findings indicate that low-level dietary supplementation to reduce enteric emissions is difficult in grazing systems due to inconsistent animal intake and that growth implants could be used as a strategy to improve growth performance and reduce EI of steers grazing improved pasture., Competing Interests: The authors affirmatively acknowledge that they were free from influence by any funding sources or their employees that would result in any conflict of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)