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Feeding behavior traits including daily feeding duration (FD), daily feeding head down time (HD), average feeding duration per feeding event (FD_AVE), average feeding head down time per feeding event (HD_AVE), feeding frequency (FF), and meal eating rate (ER) were analyzed to estimate their phenotypic and genetic correlations with feed intake, growth performance, residual feed intake (RFI), ultrasound, and carcass merit traits in Angus and Charolais finishing steers. Heritability estimates for FD, HD, FD_AVE, HD_AVE, FF, and ER were 0.27 ± 0.09 (SE), 0.25 ± 0.09, 0.19 ± 0.06, 0.11 ± 0.05, 0.24 ± 0.08, and 0.38 ± 0.10, respectively, in the Angus population and 0.49 ±0.12, 0.38 ± 0.11, 0.31 ± 0.09, 0.29 ± 0.10, 0.43 ± 0.11, and 0.56 ± 0.13, respectively, in the Charolais population. In both the Angus and Charolais steer populations, FD and HD had relatively stronger phenotypic (0.17 ± 0.06 to 0.32 ± 0.04) and genetic (0.29 ± 0.17 to 0.54 ±0.18) correlations with RFI in comparison to other feeding behavior traits investigated, suggesting the potential of FD and HD as indicators in assessing variation of RFI. In general, feeding behavior traits had weak phenotypic correlations with most of the ultrasound and carcass merit traits; however, estimated genetic correlations of the feeding behavior traits with some fat deposition related traits were moderate to moderately strong but differed in magnitude or sign between the Angus and Charolais steer populations, likely reflecting their different biological types. Genetic parameter estimation studies involving feeding behavior traits in beef cattle are lacking and more research is needed to better characterize the relationships between feeding behavior and feed intake, growth, feed utilization, and carcass merit traits, in particular with respect to different biological types of cattle. [ABSTRACT FROM AUTHOR]

In beef cattle, phenotypic data that are difficult and/or costly to measure, such as feed effi-ciency, and DNA marker genotypes are usually avail-able on a small number of animals of different breeds or populations. To achieve a maximal accuracy of genomic prediction using the phenotype and genotype data, strategies for forming a training population to predict genomic breeding values (GEBV) of the selec-tion candidates need to be evaluated. In this study, we examined the accuracy of predicting GEBV for residual feed intake (RFI) based on 522 Angus and 395 Charo-lais steers genotyped on SNP with the Illumina Bovine SNP50 Beadchip for 3 training population forming strategies: within breed, across breed, and by pooling data from the 2 breeds (i.e., combined). Two other sce-narios with the training and validation data split by birth year and by sire family within a breed were also inves-tigated to assess the impact of genetic relationships on the accuracy of genomic prediction. Three statistical methods including the best linear unbiased prediction with the relationship matrix defined based on the pedi-gree (PBLUP), based on the SNP genotypes (GBLUP), and a Bayesian method (BayesB) were used to predict the GEBV. The results showed that the accuracy of the GEBV prediction was the highest when the prediction was within breed and when the validation population had greater genetic relationships with the training pop-ulation, with a maximum of 0.58 for Angus and 0.64 for Charolais. The within-breed prediction accuracies dropped to 0.29 and 0.38, respectively, when the vali-dation populations had a minimal pedigree link with the training population. When the training population of a different breed was used to predict the GEBV of the validation population, that is, across-breed genomic prediction, the accuracies were further reduced to 0.10 to 0.22, depending on the prediction method used. Pool-ing data from the 2 breeds to form the training popula-tion resulted in accuracies increased to 0.31 and 0.43, respectively, for the Angus and Charolais validation populations. The results suggested that the genetic rela-tionship of selection candidates with the training popu-lation has a greater impact on the accuracy of GEBV using the Illumina Bovine SNP50 Beadchip. Pooling data from different breeds to form the training popula-tion will improve the accuracy of across breed genomic prediction for RFI in beef cattle. [ABSTRACT FROM AUTHOR]

Energy expenditure is a physiological process that may be closely associated with residual feed intake (RFI). The maintenance energy (MEM) EPD was developed by the Red Angus Association of America (RAAA) and is used as an indicator of energy expenditure. The objectives of this study were to evaluate and quantify the following relationships using progeny of Red Angus (RA) sires divergent for MEM EPD: 1) postweaning RFI and finishing phase feed efficiency (FE), 2) postweaning RFI and end-product quality, and 3) postweaning RFI and sire MEM EPD. A total of 12 RA sires divergent for MEM EPD were chosen using the RAAA-generated MEM EPD values and were partitioned into 2 groups: high MEM EPD (≥4 Mcal/mo) and low MEM EPD (<4 Mcal/mo), based on the breed average of 4 Mcal/mo. Commercial crossbred cows were inseminated to produce 3 cohorts of progeny, which were tested for postweaning RFI (cohorts 1, 2, and 3) and finishing phase FE (cohorts 1 and 3). Results indicate that postweaning RFI and finishing phase FE of steer progeny tended to be positively correlated (r = 0.38; P = 0.06) in cohort 1 and were positively correlated (r = 0.50; P = 0.001) in cohort 3. In addition, postweaning RFI was not phenotypically correlated (P > 0.05) with any carcass traits or end-product quality measurements. Sire MEM EPD was phenotypically correlated (P < 0.05) with carcass traits in cohort 1 (HCW, LM area, KPH, fat thickness, and yield grade) and cohort 2 (KPH and fat thickness). Since variation in measured LM area was not explained by the genetic potential of rib eye area EPD, and therefore, the observed correlation between sire MEM EPD and measured LM area may suggest an association between MEM EPD and LM area. A correlation (r = 0.24; P = 0.02) was observed between postweaning RFI and ultrasound intramuscular fat percentage in cohort 2 but was not detected in cohorts 1 or 3. In addition, no phenotypic relationship was observed (P > 0.05) between progeny postweaning RFI and sire MEM EPD. Therefore, results suggest 1) RFI measured during the postweaning growth phase is indicative of FE status in the finishing phase, 2) neither RFI nor sire MEM EPD negatively affected carcass or end-product quality, and 3) RFI and sire MEM EPD are not phenotypically associated. [ABSTRACT FROM AUTHOR]

ABSTRACT: No genetic parameters for performance and feed efficiency traits are available for Irish performance-tested bulls. The objective of this study was to determine the phenotypic and genetic variation for feed intake, BW, ADG, and measures of feed efficiency including feed conversion ratio (FCR), relative growth rate, Kleiber ratio, residual BW gain (RG), and residual feed intake (RFI). Observations were available on up to 2,605 bulls for each trait from one test station across 24 yr; breeds included in the analyses were Aberdeen Angus (AN), Charolais (CH), Hereford, Limousin (LI), and Simmental. The test period was at least 70 d. Bulls were individually offered concentrates ad libitum, with a restricted forage allowance. Differences in performance and feed efficiency existed among breeds. For example, AN, on average, ate 0.04 kg of DM/d more than CH but had ADG of 0.14 kg/d less over the 70-d test period. Results showed LI and CH were the most efficient breeds when efficiency was defined as FCR or RFI. When animals were partitioned into groups based on high, medium, or low RFI, the low RFI (i.e., most efficient) group were also the more efficient as defined by RG and FCR. The low RFI group had the same ADG as the medium group and a greater ADG (P < 0.01) than the high group (1.67 vs. 1.66 and 1.63 kg/d); yet they ate 0.67 kg of DM/d less (P < 0.001) than the medium RFI group and 1.22 kg of DM/d less (P < 0.001) than the high RFI (i.e., least efficient) group. Genetic parameters for all performance and efficiency measures were estimated across breeds using linear animal mixed models; heritability estimates for feed efficiency traits ranged from 0.28 ± 0.06 (RG) to 0.45 + 0.06 (RFI). An additional series of analyses included a maternal com- ponent in the model; maternal heritability estimates for feed efficiency traits ranged from 0.05 ± 0.03 (RG) to 0.11 ± 0.05 (relative growth rate). Genetic correlations between most of the different feed efficiency measures were strong. Results from this study indicate significant genetic differences in performance and some measures of feed efficiency among performance-tested beef bulls. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DM1, with predicted DM1 determined by linear regression of DM1 on mid-test BW0.75 (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DM1, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R2 (0.578 vs. 0.534) and accounted for 9% of the variation in DM1 not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DM1 and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition. [ABSTRACT FROM AUTHOR]

The objectives of this study were to characterize feed efficiency traits and to examine phenotypic correlations between performance and feeding behavior traits, and ultrasound measurements of carcass composition in growing bulls. Individual DM1 and feeding behavior traits were measured in Angus bulls (n = 341; initial BW = 371.1 ± 50.8 kg) fed a corn silage-based diet (ME = 2.77 Mcal/kg of DM) for 84 d in trials 1 and 2 and for 70 d in trials 3 and 4 by using a GrowSafe feeding system. Meal duration (min/d) and meal frequency (events/d) were calculated for each bull from feeding behavior recorded by the GrowSafe system. Ultrasound measures of carcass 12th-rib fat thickness (BF) and LM area (LMA) were obtained at the start and end of each trial. Residual feed intake (RFIp) was computed from the linear regression of DM1 on ADG and midtest BW0.75 (metabolic BW, MBW) with trial, trial by ADG, and trial by midtest BW0.75 as random effects (base model). Overall ADG, DM1, and RFIp were 1.44 (SD = 0.29), 9.46 (SD = 1.31), and 0.00 (SD = 0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of BW gain in BF and LMA in the base model increased R² (0.76 vs. 0.78) and accounted for 9% of the variation in DM1 not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted residual feed intake (RFIc) were moderately correlated with DM1 (0.60 and 0.55, respectively) and feed conversion ratio (FCR; 0.49 and 0.45, respectively), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78, respectively), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not with RFIc. Gain in LMA was weakly correlated with RFIp (0.17) and FCR (-0.19), but not with PEG or RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp and accounted for 35% of the variation in DM1 not explained by MBW, ADG, and ultrasound traits (RFIc). These results suggest that adjusting residual feed intake for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain. [ABSTRACT FROM AUTHOR]