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Residual feed intake (RFI), a metric of feed efficiency, is moderately heritable and minimally associated with body size and productivity, making it an ideal trait for investigation as a selection criterion to improve feed efficiency of growing cattle. The objective of this research was to characterize the inter-animal variation in biological processes of growing cattle selected to be divergent in RFI. Holstein heifers [n = 55; body weight (BW) = 351 ± 64 kg) with low- (n = 29) or high- (n = 26) genomically enhanced RFI (RFIg) were selected from a contemporary group of 453 heifers. Heifers were assigned to 1 of 2 pens, equipped with electronic feed bunks and a GreenFeed gaseous-exchange measurement system. Individual dry matter intake (DMI) and feeding behavior data were collected for 84-d. Body weight was measured weekly, and spot fecal samples collected at weighing. Phenotypic RFI (RFIp) was calculated as the residual from regression of DMI on ADG and mid-test BW0.75. On d 70 of the study a rumen fluid sample was collected via esophageal tubing. Blood samples were collected and analyzed for complete blood count (CBC). A mixed model including the fixed effect of RFIg classification and random effect of pen was used to evaluate the effect of RFIg classification on response variables. There were no differences (P > 0.05) in BW and ADG for heifers with divergent RFIg; however, low RFIg heifers consumed 7.5% less (P < 0.05) feed per day. Consequently, low RFIg heifers exhibited a more favorable (P < 0.05) RFIp (-0.188 vs 0.211 kg/d, respectively). Low RFIg heifers exhibited more favorable feeding behavior, with 8.7% fewer (P < 0.05) bunk visit events per day and an 11.2% slower (P ≤ 0.05) eating rate. Low RFIg heifers had 12.5% greater (P < 0.05) total rumen volatile fatty acid concentrations than high RFIg heifers, indicating potentially enhanced microbial fermentation and improved efficiency of feed utilization. Low RFIg heifers had 8.2% less (P < 0.05) methane emissions (g/d), 6.3% less (P < 0.05) carbon dioxide production (g/d), and 6.1% less (P < 0.05) heat production (Mcal/d) calculated according to Brouwer (1965) than high RFIg heifers. Dry matter digestibility did not differ (P > 0.05) between heifers with divergent RFIg. Overall, heifers selected to be more feed efficient exhibited more favorable energy efficiencies and feed efficiency phenotypes. To quantify the variation in RFIg explained by feeding behavior, gas flux, digestibility and rumen fermentation, and CBC partial least squares regression models were developed. Feeding behavior accounted for the largest proportion of variation in RFIg (28.8%). Upon sequential addition of gas flux, digestibility and rumen fermentation, and CBC to feeding behavior, 56.3% of the variation in RFIg was accounted for. Identifying the magnitude at which metabolic processes influence inter-animal variation in efficiency of nutrient utilization provides opportunities to discover valuable candidate biomarkers for selection of more feed efficient cattle. [ABSTRACT FROM AUTHOR]

Bovine respiratory disease (BRD) contributes to high rates of mortality and morbidity among feedlot animals. Thus, there is a need to discover robust predictive biological indicators of infection status and disease severity in feedlot cattle. This study aimed to explore the use of 1 H nuclear magnetic resonance (NMR) based metabolite profiling to characterize serum molecular markers associated with a viralbacterial respiratory disease challenge in beef cattle. Crossbred beef steers [n = 24; initial body weight (BW) = 293 kg) were inoculated intranasally with bovine herpes virus-1 (2×108 PFU) and intratracheally with Mannheimia haemolytica (MH, 2.15×1010 CFU) on d -3 and 0, respectively (n = 16; MH-challenge), or similarly inoculated with phosphate-buffered saline (n = 8; Control-challenge). Blood was collected via jugular venipuncture on d -3, -1, 0, 2, 3, 5, 7, 10, and 14 relative to MH challenge for complete blood count and haptoglobin analysis, with additional serum samples stored at -80°C for subsequent metabolomic analysis. Continuously recorded variables included rumen temperature, activity, rumination, dry matter intake, and feeding behavior. Wottlin et al. (2020) reported that rumen temperature was increased (P < 0.04) in MH-challenged steers until d 6 post-MH inoculation (40.8 vs 39.3°C in MH-challenged and Controlchallenged steers several hours post-MH inoculation). Dry matter intake was reduced (P < 0.01) by 42% in MH-challenged compared with Control-challenged steers during the 14-d post-MH inoculation period. Further, haptoglobin concentrations were increased (P < 0.05) in MH-challenged steers from d 2 to 7 of the post-MH inoculation period. Serum samples underwent small molecule metabolite extraction and untargeted ¹ H NMR metabolomics. The ¹ H NMR spectra of serum metabolites were evaluated for this study, resulting in the unambiguous identification and quantification of 64 polar metabolites. Univariate analysis was conducted to examine the effect of the MH challenge on relative metabolite concentrations between d 2 and 5 relative to MH challenge, indicating differences between metabolites of MH-challenge and Control-challenged steers. However, multivariate analysis using unsupervised 2-dimensional principal component analysis (2D-PCA) could not differentiate MH-challenged from Control-challenged steers based on distinct serum metabolite profiles. Results indicate the potential of specific metabolites to indicate BRD infected cattle; however, a larger cohort of cattle and expanded metabolite profile coverage may be required to more fully differentiate between BRD vs healthy cohorts. Opportunities exist to further investigate the role of metabolomics to discover robust early biological indicators that are predictive of the onset of BRD in feedlot cattle. [ABSTRACT FROM AUTHOR]

This review delves into the intricate realm of ruminal microbes, shedding light on their complexity beyond previously recognized dimensions. Existing publications have probed the essential facets of these microorganisms on a finer scale than previously acknowledged. Mathematical models have emerged to simulate the behavior of approximately 200 distinct bacterial species, 25 genera of ciliate protozoa, and five genera of anaerobic fungi, constituting about 10% of the total viable bacteria in the rumen. However, the expansive diversity and density of rumen microbes challenge the complete characterization of species or genera in relation to substrates or end products. Consequently, continuous revision and re-engineering of mathematical models become imperative. In the context of ruminants, prevalent models often categorize bacteria into fiber-fermenting and nonfiber-fermenting groups. An additional subgroup featuring hyper-ammoniaproducing bacteria has been proposed, but its explicit integration into nutrition models remains unexplored. Furthermore, incorporating a more mechanistic evaluation of protozoa and fungal growth may be warranted to improve nutrition models. The time horizon and intervals at which models are constructed present another critical consideration, with feed efficiency variations among ruminants believed to be closely tied to differences in the ruminal microbiota. Addressing immediate concerns, this review underscores the need for a comprehensive exploration of factors influencing microbial growth in the rumen. Several indices have been suggested and adopted to predict microbial efficiencies, but they may provide simplification for practical application. Thus, a mechanistic approach should be considered to remove dependencies between estimates and improve predictive accuracy and precision. While artificial intelligence holds promise in elucidating gaps within empirical and mechanistic models, the generation of accurate, vetted datasets is paramount. Furthermore, this review posits that factors such as recycled nitrogen, endotoxins, and microbial population dynamics (i.e., cross-feeding and competition) may be limiting our understanding of microbial growth, suggesting the necessity of modeling these intricacies concurrently to achieve a more nuanced comprehension. This multifaceted approach aims to propel the understanding of ruminal microbial dynamics into new frontiers, paving the way for more informed and effective modeling in the future. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the differences in performance, feed efficiency, feeding behavior and gaseous exchange (methane, carbon dioxide and oxygen) in replacement beef heifers with divergent phenotypes for residual feed intake (RFI). Crossbred beef replacement heifers [n = 63; initial body weight (BW) = 277 ± 21 kg] were blocked by BW and assigned to 1 of 2 pens each equipped with electronic feed bunks (GrowSafe Systems) and GreenFeed gaseous-exchange measurement systems (GEM; C-Lock). Heifers were fed a corn-silage based ration twice daily. Individual dry matter intake (DMI), feeding behavior, and gas flux data were collected for 70 d and BW measured weekly. Carcass ultrasound data were collected at the beginning and end of the study. Residual feed intake was calculated as the residual from the regression of DMI on ADG and mid-test BW0.75 and heifers assigned to low-, medium-, and high-RFI classes (± 0.5 SD from the mean RFI). A mixed model with RFI class as fixed effect and pen as a random effect was used for data analysis. There were no differences due to RFI class in BW and ADG. However, low-RFI heifers consumed 16% less (P < 0.001) DMI and had more favorable gain to feed (G:F) then high-RFI heifers. High-RFI heifers had a greater (P < 0.05) backfat gain during the 70-d study, with backfat gain accounting for an additional 4.2% of the variation in DMI. LowRFI heifers exhibited more favorable feeding behavior, with 10.4% fewer (P = 0.057) bunk visit events and spent numerically less time at the feed bunk (103 vs 122 min/d) compared with high-RFI heifers. Methane emissions (g/d) did not differ between heifers with divergent RFI (P = 0.138; 129 vs 140 g/d in low- and high RFI heifers respectively), however, methane yield (g/kg DMI) was 9% greater (P < 0.05) in low- compared with high-RFI heifers. Additionally, low-RFI heifers produced 7.9% less (P < 0.05) carbon dioxide (g/d) and consumed 6.9% less (P < 0.05) oxygen than high RFI heifers. Further research is warranted to investigate the biological mechanisms influencing RFI and the effects of selection for RFI as a strategy to mitigate reduce greenhouse gas emissions from cattle production systems. [ABSTRACT FROM AUTHOR]

Livestock methane (CH4) emissions total over 3 billion tonnes per year of carbon dioxide equivalents (CO2e) and are responsible for approximately 6% of total annual greenhouse gas emissions. The contribution of livestock CH4 emissions are only to be exacerbated as the global demand for meat and dairy products increases. Greater than 75% of livestock CH4 emissions are generated in dispersed production environments (e.g., cow-calf and stocker segments), which are not addressable by methane mitigation strategies requiring constant inputs. Thus, strategies that fit into standard agronomic practices, in particular dispersed production environments, are urgently needed to address the increasing carbon footprint associated with livestock production. Methane-reducing vaccines are a promising solution for addressing this need, due to their longevity of action, low cost, and ease of integration into standard agronomic practices, which could lower the barrier for adoption. Thus, this study aimed to assess the effects of a prototype vaccine on total and antigen-specific immune response, CH4 yield, and average daily gain (ADG) in cattle. Angus crossbred steers [n = 20; initial body weight (BW) = 537 ± 15 kg) fed on a high-forage diet were randomly assigned to either placebo- or vaccine-treated groups blocked by BW, breed, and feed intake. Steers were subcutaneously inoculated (2 mL dose) in the anterior region of the neck. Blood and saliva samples were collected, and total sera and salivary immunoglobulin (Ig) G and IgA were quantified using ELISA (Bethyl laboratories, Montgomery, TX). Antigen-specific sera IgG was measured using ELISA. Daily CH4 emissions and dry matter intake (DMI) were measured using GreenFeed systems (C-Lock Inc. Rapid City, SD) and GrowSafe feed bunks (Vytelle, Lenexa, KS), respectively. Body weights were recorded bi-weekly. Total sera IgA and IgG did not differ between the placebo-treated and vaccinated steers (P = 0.584 and P = 0.425, respectively), nor did total salivary IgA and IgG (P = 0.577 and P = 0.548, respectively). However, antigen-specific sera IgG did significantly increase following booster vaccination in the vaccinated steers, as compared with placebotreated steers (d 0 vs. d 28; P < 0.001). CH4 yield was significantly reduced in vaccinated steers following booster vaccination despite significantly increasing in placebo-treated steers over the same period (P = 0.002). This reduction in CH4 yield was not associated with a reduction in DMI nor ADG (P = 0.181 and P = 0.314, respectively), suggesting that vaccination did not negatively affect treated animals. These findings underscore the potential of vaccine-based solutions to mitigate the environmental impact of livestock CH4 emissions, especially from dispersed production environments where current options for mitigation strategies are limited. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects of breed and days on trial (DOT) on feeding behavior traits in two breeds of growing goats. Nineteen female goats [n = 10 Alpine; n = 9 Spanish, with average initial ages of 360 d and 352 d, and body weight (BW) of 38.8 ± 2.8 kg and 35.5 ± 3.1 kg, respectively], were randomly assigned within the breed to one of two non-adjacent pens (5 goats/ pen), each equipped with GrowSafe feed bunks. A pelletized total mixed ration (TMR) was fed twice per day and goats had ad libitum access to feed, water, and mineral block throughout the 84-d trial. Feeding behavior traits, including feed intake, bunk visit frequency (BVF), head-down duration (HDD), and dry matter intake (DMI) were collected daily using the GrowSafe feeding system. A 14-d interval was used to derive feed behavior traits of individual goats at 42, 56, 70, and 84 DOT. Data were analyzed using a repeated-measures model with a fixed effect of breed, DOT as a repeated measure, and breed x DOT interaction with pen as a random effect. Alpine goats had greater (P < 0.05) initial and final BW (37.6 kg and 51.7 kg, respectively) than Spanish goats (34.7 kg and 46.5 kg, respectively) although DMI (P = 0.10; 1.73 ± 0.31 and 1.39 ± 0.18 kg/d) did not differ. There was not a significant difference (P > 0.05) between breeds for frequency of bunk visits (21.1 vs. 18.6) and bunk duration (P > 0.05). Similarly, the effect of breed on DMI (27.1g/min vs. 22.8 g/min) was non-significant (P > 0.05). Furthermore, breed did not significantly (P > 0.05) affect HDD (31.3 min/d vs 31.9 min/d). However, there was a significant interaction (P < 0.05) between breed and DOT for HDD. In addition, significant differences (P < 0.05) were observed due to the length of DOT for BVD, bunk visit duration, HDD, and eating rate (g/min). Our results suggest that Spanish goats tended to visit feed bunks more frequently per day and tended to consume less feed per visit than their counterpart Alpine goats, and the feeding behaviors of goats change with age. However, further research is warranted to determine changes in the feeding behavior of goats in different production cycles. [ABSTRACT FROM AUTHOR]

Visual observations of competitive feeding behavior in cattle have been associated with animal productivity, health, and social hierarchy. However, human visual observations are time consuming, limiting the number of animals that can be evaluated. The objective of this study was to develop and assess an algorithm to detect disruptive feed bunk replacement events using feeding event data acquired from the Vytelle SENSE feed intake measurement system. Crossbred beef steers (N = 20) fed a grower diet were housed in one of two pens each equipped with three electronic feed bunks and a video recorder. A trained video observer recorded all feed bunk replacement events (when an actor animal displaced a reactor animal from the feed bunk and occupied the same feed bunk within a specified time interval, termed as the replacement criterion) and other agonistic activities at the feed bunk during a 4-d period. The Vytelle SENSE feed intake measurement system recorded the start and end timestamps of individual bunk visit (BV) events of animals. An algorithm was developed to determine replacement events based on the start and end times of consecutive BV events. Using video observation as the gold standard, the recall, precision, and F-score of the algorithm was calculated corresponding to time intervals from 1 to 60 s. The optimum replacement criterion was determined to be ≤ 18 s and ≤ 22 s for pens 1 and 2 respectively. The recall, precision, and F-score of the algorithm using these replacement criterions were high (> 0.75). A competition index was computed for each steer, calculated as the number of actor-initiated events divided by the number of actor and reactor events at the feed bunk. Spearman's rank correlations (r s) between total visually observed agonistic interactions at the feed bunk and the replacement events detected from the electronic feeding event data using the algorithm and replacement criterion of the respective pen was determined. There were strong correlations (r s ≥ 0.71; P < 0.05) between the observed and electronic values for the number of actor and reactor events, and the competition index. These results demonstrate the potential to quantify disruptive feed bunk replacement events in confined beef cattle using electronically collected feeding event data from the Vytelle SENSE feed intake measurement system. • Sensor technologies can enable objective assessment of behavior of large groups of animals. • An algorithm was developed to quantify feed bunk replacement events using electronic feeding data. • There is potential for an electronic feeding system to quantify feed bunk replacement events. [ABSTRACT FROM AUTHOR]

The objectives of this study were to examine the effects of gender and breed type on performance, feed efficiency, and feeding behavior traits in growing goats. The trial was conducted with 36 intact male (n = 16) and female (n = 20) goats of 4 breed types;12 purebred Spanish, 12 F1 Spanish x Boer (dam-sire), 8 F1 Boer x Spanish, and 4 purebred Boer. Goats with initial BW of 30.9 ± 6.0 kg and 38.8 ± 7.4 kg for females and males, respectively, were fed a concentrate diet in pens equipped with electronic feed bunks (GrowSafe System). Individual dry matter intake (DMI) and feeding behavior traits were collected daily for 44 d and BW measured weekly. Residual feed intake (RFI) was calculated as the residual from the regression of DMI on ADG and mid-test BW0.75. Feeding behavior traits evaluated were frequency and duration of bunk visit (BV) events, head-down (HD) duration, BV eating rate (BVER), and day-to-day variation of these traits, defined as the root mean squared error (RMSE) from linear regression of each trait on the day of trial. A mixed model (JMP) with fixed effects of gender, breed type, and gender x breed type interaction with pen as a random effect was used. Gender x breed type interactions were not significant for any traits. Male goats had heavier (P < 0.01) initial and final BW, but similar ADG during the trial. Male goats consumed more (P < 0.05) DMI, but had similar F:G and RFI compared with female goats. Gender did not affect feeding behavior traits, but male goats had greater BVER and more (P < 0.05) day-to-day variation in DMI than female goats. Purebred Boer goats had heavier (P < 0.05) initial and final BW and greater ADG than purebred Spanish and both F1 crosses. However, DMI and RFI were not affected by breed type. G:F was greater (P < 0.05) in Boer and Boer x Spanish goats (0.183, 0.153) than Spanish goats (0.115), with Spanish x Boer (0.132) goats being intermediate. Breed type did not affect feeding behavior traits in this trial. Minimal effects of gender and breed type on feed efficiency were detected in growing goats in this trial. Further research is warranted to examine effects of breed type on life-cycle feed efficiency including growing goats and female goats during pregnancy and lactation. [ABSTRACT FROM AUTHOR]

Virginiamycin (VM) possesses antimicrobial properties due to its blocking of protein synthase in Gram-positive bacteria, allowing it to reduce lactic acidosis and the incidence of liver abscesses in ruminants. Ruminal acidosis is a common metabolic disorder that affects feedlot and dairy cattle and occurs when the supply of organic acids from fermentation exceeds its absorption and degradation, accumulating acid content in the rumen. The objective of this study was to evaluate the effects of three different doses of VM administration on in vivo and in vitro ruminal digestion kinetics of beef steers consuming a high-grain diet [metabolizable energy (ME): 2.99 Mcal/kg; Crude Protein (CP): 15.2 % dry matter basis (DM)]. Nine ruminally cannulated British-crossbred steers (596 ± 49 kg) were assigned to this experiment. Animals were housed in three pens (n = 3/pen) equipped with a Calan gate feed system and water trough. Pens were enrolled in a 3×3 Latin square design containing three periods of 16 d, and a 5-d washout interval between periods. Dietary treatments consisted of VM administration at 0 mg/d (VM0), 180 mg/d (VM180), and 240 mg/d (VM240). During d 15 and 16 of each period, about 600 mL of rumen fluid was collected before (0 h) and at 4, 8, 12, and 16 h relative to the morning feed (0730 h) pH and redox potential (Eh) measurements were taken immediately after collection using a portable pH and redox meter, and subsamples were taken for volatile fatty acids (VFA), and NH3-N analyses. During the 4-h post-morning feed rumen collection, rumen inoculum was utilized to perform in vitro gas production (IVGP) measurements. All statistical procedures were performed using SAS software where steer was considered the experimental unit, and period and square were included as random. Acetate, propionate, and total VFA did not differ among treatments (P = 0.50), whereas butyrate increased linearly (P = 0.033) as the VM dose increased. Acetate:propionate ratio did not differ among treatments (P = 0.273). Lactate concentration decreased linearly (P = 0.027) as the VM dose increased; likewise, pH increased linearly (P = 0.019) as the VM dose increased. Branched-chain VFA and NH3-N concentrations increased linearly (P = 0.056) as the VM dose increased. The total and rate of gas production were similar among treatments (P = 0.161). However, second-pool gas production increased linearly as VM inclusion increased (P = 0.023). The in vitro neutral detergent fiber digestibility did not differ among treatments (P = 0.984). The provision of VM altered the rumen dynamics in a dose-dependent manner. Animals consuming high-grain diets will likely promote rumen health through a more stable pH and fermentation profile. [ABSTRACT FROM AUTHOR]

Rumen microbes serve a vital role in feed utilization of ruminant animals, suggesting the potential of rumen microbiota to influence inter-animal variation in nutrient utilization. There is limited knowledge surrounding the influence of the rumen bacterial community in animals selected based on feed efficiency. The objective of this study was to examine the differences in the rumen bacterial community in replacement Holstein heifers with divergent genomically enhanced breeding values for residual feed intake (RFIg). Genomic breeding values for RFIg were based on RFI phenotypes of 6,563 growing Holstein heifers from STgenetics ongoing EcoFeed research program. Holstein heifers (n = 55; initial BW = 351 ± 64 kg) with low RFIg (n = 29) or high RFIg (n = 26) were selected from a contemporary group of 453 heifers (RFIg = -0.023 ± 0.211 kg/d). These heifers were assigned to 1 of 2 pens, equipped with electronic feedbunks (GrowSafe Systems) and a GreenFeed gaseous-exchange measurement system (C-Lock). Individual DMI was collected for 84-d and BW measured weekly to determine phenotypic RFI. On d-70 of the study, a rumen sample was collected from each animal via esophageal tubing and bacterial community composition determined through 16S rRNA gene sequencing of the V4 region. A total of 523 amplicon sequence variants (ASVs) were observed among the 55 samples, with the average reads per sample of 54,107 ± 42,688 across samples. To examine the rumen bacterial composition, permutational multivariate analysis of variance (PERMANOVA) utilizing the weighted and unweighted Unifrac distance matrix was used. Utilizing the weighted Unifrac no differences (P = 0.513) were observed in the bacterial composition of the rumen content between heifers with divergent RFIg; however, utilizing the unweighted Unifrac differences (P = 0.031) were identified in the bacterial composition between heifers with divergent RFIg. Based on alpha diversity metrics, observed ASVs displayed greater (P = 0.015) bacterial richness in high-compared with low-RFIg heifers; however, there was no difference (P = 0.500) in the Shannon diversity index between heifers with divergent RFIg. ASV level classification of the most differentially abundant (P < 0.05; log2-fold change > 1) ASVs demonstrated that three ASVs from the bacterial family Prevotellaceae, and one ASV from the bacterial family Ruminococcaceae was predominant in high-compared with low-RFIg heifers. Additionally, one ASV belonging to the family Prevotellaceae was predominant in low-heifers compared with their high-RFIg counterparts. Results from this study indicate greater enrichment of ruminal bacteria in high RFIg cattle, with ASVs from the Prevotellaceae and Ruminococcaceae families differing between heifers with divergent RFIg. Opportunities exist to further investigate the role of the rumen microbiome in selection of cattle based on genomic RFI, and to assess associations between specific bacterial ASVs and phenotypic feed efficiency traits in cattle. [ABSTRACT FROM AUTHOR]

The objectives of this study were to evaluate the effects of breed and days on trial (DOT) on feed intake, growth rate, and feed efficiency of growing goats. Nineteen female goats (10 Alpine and 9 Spanish) with an initial BW of 38.8 ± 2.8 and 35.5 ±3.1 kg, respectively, were randomly assigned within breed to one of two pens (5 goats/pen), each equipped with GrowSafe feed bunks. A pelletized total mixed diet (TMD) was fed twice per day and goats had ad libitum access to feed and water throughout the 84-d trial. Daily feed intake (DMI) was collected with GrowSafe automated feeding system, and BW was measured biweekly. Linear regression of 14-d BW on DOT was used to derive ADG, mid-test metabolic BW (MBW) and expected DMI of individual goats at 42, 56, 70, and 84 DOT. Expected DMI was predicted by linear regression of DMI on MBW and ADG, with RFI calculated as a difference between actual and expected DMI for each DOT. Data were analyzed using a repeated-measures model with a fixed effect of breed, DOT as a repeated measure, and breed x DOT interaction with a pen as a random effect. The interaction was not significant for either of the response variables. Alpine goats had greater (P < 0.05) initial and final BW (37.6 kg and 51.7 kg, respectively) than Spanish goats (34.7 kg and 46.5 kg, respectively) although ADG (0.233 kg/d vs 0.191 kg/d) did not differ. DMI (P = 0.10) and RFI (P = 0.09) tended to be greater in Alpine than in Spanish goats (0.57 kg vs -0.64 kg). However, G:F was not affected (P > 0.70) by breed. As DOT increased from 42 to 84, MBW increased, while ADG, DMI, and G:F decreased. Further research is warranted to determine changes in phenotypic variances of ADG and DMI to determine the minimal DOT needed to accurately measure feed efficiency in growing goats. Our results suggest that Spanish goats tended to consume less feed and tended to be more efficient (negative RFI) than their counterpart Alpine goats. Further research is needed to compare the lifecycle efficiency of Alpine and Spanish goats. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the differences in performance, feed efficiency, and greenhouse gas emissions in Holstein heifers with divergent genomic residual feed intake (RFIg). Holstein heifers (n = 55; initial BW = 351 ± 64 kg) were classified as either low RFIg (n = 29) or high RFIg (n = 26) based on RFIg values determined from their genomic breeding values (Ecofeed index, STgenetics). Heifers were blocked by RFIg, stratified by BW and assigned to 1 of 2 pens, each equipped with 4 electronic feedbunks (GrowSafe Systems), with 1 pen equipped with a GreenFeed realtime gaseous-exchange measurement system (GEM; C-Lock). Heifers were fed a corn-silage based total mixed ration twice daily. Individual dry matter intake (DMI) was collected for 84 d and BW measured weekly. Phenotypic residual feed intake (RFIp) was calculated as the residual from the regression of DMI on average daily gain (ADG) and mid-test BW0.75. As only 1 of the 2 pens had a GEM system, during the 84-day study heifers were rotated between the two pens at 14 day intervals resulting in each group of heifers having three 14-day gaseous exchange measurement periods. A time series analysis of gaseous exchange measurements, with a repeated measure of measurement period, fixed effect of RFIg class and random effect of pen was conducted. A mixed model with RFIg class as fixed effect and pen as a random effect was used for analysis of the other response variables. There were no differences in initial or final BW and ADG for heifers with divergent RFIg; however, the low RFIg heifers consumed 7.3% less (P < 0.05) feed per day than their high RFIg counterparts. Consequently, low RFIg heifers exhibited a more favorable (P < 0.05) RFIp, with a RFIp of -0.188 and 0.211 kg/d for low and high RFIg heifers, respectively. There were no RFIg class by measurement period interactions (P > 0.10) for the greenhouse gas emissions measured. Low RFIg heifers had 7.7% less (P < 0.05) methane emissions (g/d) and 6.1% less (P < 0.05) carbon dioxide production (g/d) than their high RFIg counterparts. However, methane yield (g methane/kg DMI) was similar (P > 0.05) for low and high RFIg heifers. These results indicate that selection for low RFIg has the potential to identify cattle with favorable feed efficiency phenotypes. Additionally, selection based on RFIg provides the opportunity to produce cattle with fewer greenhouse gas emissions. Further research is warranted into selection based on RFIg through genomic indexes to improve feed efficiency and mitigate the environmental impact of cattle production. [ABSTRACT FROM AUTHOR]

Visual observations of social behavior and dominance relationships in cattle have been used to examine associations with productivity and well-being. This method is time consuming limiting the number of animals that can be evaluated. The objective of this study was to validate an algorithm to quantify feedbunk replacement events using data from an electronic feeding system. Crossbred beef steers (n = 20) fed a grower diet were housed in 1 of 2 pens each equipped with 3 electronic feedbunks (GrowSafe Systems) and video recorders. A trained video observer recorded all feedbunk replacement events and other agonistic activities at the feedbunk over a 4-d period (24 h/d). The electronic feeding system recorded the start and end timestamps of bunk visit (BV) events for each animal. An algorithm was developed to determine BV events deemed to be replacement events, defined as a BV event when an actor animal displaced a reactor animal from the feedbunk and occupied the same feeder within a specified period of time (replacement criterion). We calculated the recall and precision corresponding to replacement criterions from 1 to 60 s, and the optimum replacement criterion was determined to be between 18 and 20 s. The recall, precision and F-score of the algorithm using this replacement criterion were high (on average > 0.75). Furthermore, a replacement competition index was computed as a proxy for competitive feedbunk behavior, calculated as the number of actor-initiated replacement events divided by the total number of replacement events for each steer. Using Spearmans rank correlation we found high correlations (r > 0.7; P < 0.05) between the electronic and observed indices. These preliminary results demonstrate the potential of the GrowSafe system to quantify feedbunk replacement events for confined beef cattle, providing opportunities to evaluate associations between competitive feedbunk behavior and economically relevant traits. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine if the magnitude of interactive feeding activity at the feedbunk affects feed efficiency and feeding behavior patterns in beef cattle. This study used data from 498 crossbred steers (3 trials) fed high-concentrate diets in pens with electronic feed bunks (GrowSafe Systems). Timestamp data for bunk visit (BV) events were used to develop an algorithm to quantify those BV events deemed to be replacement events; Defined as those that occur when an animal displaces and replaces another animal from the feedbunk within a specified period of time (replacement criterion). For this study, a replacement criterion of ≤ 18 s was used. A replacement activity index (RAI) was computed for each steer as the number of replacement events divided by total BV events. Within pen, steers were classified into 1 of 3 phenotypes based on ± 0.5 SD from mean RAI. Steers with high RAI (> 0.5 SD from mean RAI) were hypothesized to be more interactive at the feedbunk, whereas steers with low RAI were less interactive at the feedbunk. A mixed model with RAI class as fixed effect, and trial and pen within trial as random effects was used for data analysis. The low RAI steers had 6% fewer BV events that were 12% longer (P < 0.001) in duration than high RAI steers. Additionally, eating rate (g/min) was 14% slower (P < 0.001) and time to approach the feedbunk following feed delivery 6 min longer (P < 0.001) in low vs high RAI steers. The low-RAI steers had substantially less (P < 0.01) feeding activity during peak feeding time than high RAI. Further research is warranted to evaluate interactive feeding activity at the feedbunk as a potential indicator of performance and feed efficiency in feedlot cattle. [ABSTRACT FROM AUTHOR]

Residual feed intake (RFI), a metric of feed efficiency, is moderately heritable and independent of body size and productivity, making it an ideal trait for investigation as a selection criterion to improve the feed efficiency of growing cattle. The objective of this study was to examine the differences in performance, feed efficiency, feeding behavior, gas flux, and nutrient digestibility in Holstein heifers with divergent genomically enhanced breeding values for RFI (RFIg). Holstein heifers (n = 55; BW = 352 ± 64 kg) with low (n = 29) or high (n = 26) RFIg were selected from a contemporary group of 453 commercial Holstein heifers. Heifers were rotated between 1 of 2 pens, each equipped with 4 electronic feed bunks and 1 pen with a GreenFeed emissions monitoring (GEM) system. Individual dry matter intake (DMI) and feeding behavior data were collected for 84-d. Body weight (BW) was measured weekly and spot fecal samples were collected at weighing. Phenotypic RFI (RFIp) was calculated as the residual from the regression of DMI on average daily gain (ADG) and mid-test metabolic BW (BW0.75). A mixed model including the fixed effect of RFIg classification and the random effect of group was used to evaluate the effect of RFIg classification on response variables. There were no differences (P > 0.05) in BW and ADG for heifers with divergent RFIg; however, low RFIg heifers consumed 7.5% less (P < 0.05) feed per day. Consequently, low RFIg heifers exhibited a more favorable (P < 0.05) RFIp compared to high RFIg heifers (-0.196 vs 0.222 kg/d, respectively). Low RFIg heifers had 8.7% fewer (P < 0.05) bunk visit events per day and tended to have an 11.2% slower (P < 0.10) eating rate. Low RFIg heifers had 7.7% lower (P < 0.05) methane (CH4) emissions (g/d), 6.1% lower (P ≤ 0.05) carbon dioxide (CO2) production (g/d), and 5.6% lower (P ≤ 0.05) heat production (Mcal/d) than high RFIg heifers. However, CH4 yield and CO2 yield (g/kg DMI), and heat production per unit DMI (Mcal/kg DMI) did not differ (P > 0.05) between heifers with divergent RFIg. Dry matter (DM) and nutrient digestibility did not differ (P > 0.05) between heifers with divergent RFIg. Results suggest that selection based on RFIg provides opportunities to select cattle with favorable feed efficiency phenotypes to increase the economic and environmental sustainability of the cattle industry., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)