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There is concern in the beef industry that selecting bulls for feed efficiency based on residual feed intake (RFI) may have a negative impact on bull repro-ductive performance and fertility. Here we investigated the impact of selection of bulls for low RFI on breeding soundness evaluation (BSE), reproductive performance, and fertility of bulls under natural service in multisire mating groups on pasture. Of the 412 RFI-tested bulls available, 98 (23.8%) were culled for performance, type, temperament, or other reasons, and 88 (21.4%) were culled for failing BSE, for an overall cull rate of 45.1%. From among the 314 bulls subjected to BSE, 32 (10.2%), 20 (6.4%), and 36 (11.4%) were culled for poor feet and legs, scrotal circumference, and semen quality, respectively. The BSE traits were not different (P > 0.10) between bulls categorized as either inefficient (+RFI) or efficient (-RFI), but the proportion of bulls that failed to meet the 60% minimum sperm motility requirement tended (P = 0.07) to be greater in the -RFI group than in the +RFI group (10.2% vs. 4.4%, respectively). In a subpopulation of 115 bulls, individual progressive spenn motility was greater {P < 0.05) in +RFI (85%) than -RFI (80%) bulls. A multisire natural mating experiment was conducted during 2 consecutive breeding seasons (2006 to 2007 and 2007 to 2008) using 18 +RFI and 18 -RFI bulls. The overall calving rate (calves born/cows exposed) was 72.9%. Mean number of progeny per sire was significantly greater (P <0.01) in -RFI bulls (18.3) than in +RFI bulls (11.8). Selection for feed efficiency based on RFI appears to have no detrimental impact on reproductive performance and fertility in beef bulls bred in multisire groups on pasture. However, the decreased sperm motility and the greater number of progeny per sire associated with -RFI status need further investigation. [ABSTRACT FROM AUTHOR]

This study set out to examine the genetic parameters and genetic correlations of feed efficiency traits in steers (n = 490) fed grower or finisher diets in two feeding periods. A bivariate model was used to estimate phenotypic and genetic parameters using steers that received the grower and finisher diets in successive feeding periods while a repeated animal model was used to estimate the permanent environmental effects. Genetic correlations between the grower-fed and finisher-fed regimes were 0.50 ± 0.48 and 0.78 ± 0.43 for RFI and G:F, respectively. The moderate genetic correlation between the two feeding regimes may indicate the presence of genotype-by-environment interaction (GEI) for RFI. Permanent environmental effects (expressed in percentage of phenotypic variance) were detected in the grower-fed steers for ADG (38%), DMI (30%), RFI (18%) and G:F (40%) and also in the finisher-fed steers for ADG (28%), DMI (35%), MWT (23%) and RFI (10%). Heritability estimates were 0.08 ± 0.10 and 0.14 ± 0.15 for the grower-fed steers while 0.42 ± 0.16 and 0.40 ± 17 for the finisher-fed steers for RFI and G:F, respectively. The dependency of the RFI on the feeding regime may have serious implications when selecting animals in the beef industry. Due to higher cost of grains, feed efficiency in the feedlot might be over emphasized while efficiency in the cow herd and the backgrounding segments may have less emphasis. These results may also favor the retention (for subsequent breeding) of cows whose steers were efficient in the feedlot sector. Therefore, comprehensive feeding trials may be necessary in order to provide more insight into the mechanisms surrounding GEI in steers. [ABSTRACT FROM AUTHOR]

Because of the moderate heritability and the expense associated with collection of feed intake data, effective selection for residual feed intake (RFI) would be enhanced if marker assisted evaluation were used for accurate estimation of genetic merit. In this study, a suite of genetic markers predictive of RFI, DMI and ADG were pre-selected using single marker regression analysis and the top 100 SNP analyzed further to provide prediction equations for the traits. The data used consisted of 728 spring born beef steers, offspring of a cross between a composite dam line and Angus, Charolais or University of Alberta hybrid bulls. Feed intake data was collected over a 5 yr period with 2 groups (Fall-Winter and Winter-Spring) tested every year. Training and validation data sets were obtained by splitting the data into 2 distinct sets as follows: by randomly splitting the data into training and testing sets based on sire family (split 1) in 5 replicates or by retaining all animals with no known pedigree relationships as the validation set (split 2). A total of 37,959 SNP were analyzed by single marker regression, of which only the top 100 that corresponded to a P-value < 0.002 were retained. The 100 SNP were then analyzed using random regression BLUP (RR-BLUP) and only SNP that were jointly significant (P < 0.05) were included in the final marker panels. The marker effects from the selected panels were used to derive the molecular breeding values (MBV), which were calculated as a weighted sum of the number of copies of the more frequent allele at each SNP locus, weights being the allele substitution effects. The correlation between MBV and phenotype represented the accuracy of prediction. For all traits evaluated, accuracy across breeds was low, ranging between 0.007 and 0.414. Accuracy was least in data split 2, where the validation individuals had no pedigree relationship with animals in the training data. Given the low predictive ability observed, a large number of individuals may be needed for prediction when using such an admixed population. Further, these results suggest that breed composition of the target population where the marker panels are likely to be used should be an important consideration when developing prediction equations across breeds, especially where an admixed population is used as the training dataset. [ABSTRACT FROM AUTHOR]

The benefit of using genomic breeding values (GEBV) in predicting ADG, DMI and residual feed intake (RFI) for an admixed population was investigated. Phenotypic data consisting of individual daily feed intake measurements for 721 beef cattle steers tested over 5 yr was available for analysis. The animals used were an admixed population of spring born steers, progeny of a cross between 3 sire breeds and a composite dam line. Training and validation data sets were defined by randomly splitting the data into training and testing datasets based on sire family so that there was no overlap of sires in the 2 sets. The random split was replicated to obtain 5 separate datasets. Two methods (BayesB and random regression BLUP) were used to estimate marker effects and define marker panels and ultimately the GEBV. The accuracy of prediction (the correlation between the phenotypes and GEBV) was compared between SNP panels. Accuracy for all traits was low, ranging from 0.223 to 0.479 for marker panel with 200 SNP, and 0.114 to 0.246 for marker panels with 37,959 SNP, depending on the genomic selection method used. This was less than accuracies observed to polygenic EBV accuracies, which ranged from 0.504 to 0.602. The results obtained from this study demonstrate that the utility of genetic markers for genomic prediction of RFI in beef cattle may be suboptimal. Differences in accuracy were observed between sire breeds when the RR-BLUP method was used, which may imply that the correlations obtained by this method were confounded by the ability of the selected SNP to trace breed differences. This may also suggest that prediction equations derived from such an admixed population may only be useful in populations of similar composition. Given the sample sized used in this study, there is a need for increased feed intake testing if substantially greater accuracies are to be achieved. [ABSTRACT FROM AUTHOR]

Leptin is the hormone product of the obese gene synthesized and secreted predominantly by white adipocytes. It functions as a lipostatic signal regulating BW, food intake, energy expenditure, reproduction, and certain immune system functions. Although previous studies have identified polymorphisms in the coding regions of the leptin gene in cattle that show considerable associations with feed intake, milk quality and quantity, and carcass fatness, no such associations have been reported for the leptin promoter. The current study reports associations between SNP in the 5' untranslated promoter region of the bovine leptin gene with serum leptin concentration, growth, BW, feed intake, feeding behavior, and carcass merit in hybrid cattle (n = 150). The study showed that animals with the TT genotype of a less frequent cytosine/thymine (CIT) substitution (UASMS2; frequency of thymine allele equals 0.21) detected at position 528 in the bovine leptin promoter (GenBank Accession No. AB070368) show 48 and 39% increases in serum leptin concentration (P < 0.001), 39 and 31% increases in backfat thickness (P < 0.001), and 13 and 9% increase in marbling score (P = 0.01), compared with CC or CT genotypes, respectively. Animals with the TT genotype also show significantly higher feed intake (P < 0.001), growth rate, metabolic BW (P < 0.05), and live weight at slaughter (P < 0.10). Animals with the GG genotype of a more frequent cytosine/guanine (C/G) substitution (UASMS3; frequency of G allele equals 0.59) at position 1759 in the bovine leptin promoter (GenBank Accession No. AB070368) also show higher feed intake (P = 0.00 1), growth rate (P < 0.10), and BW (P < 0.01). The thymine allele of UASMS2 and the guanine allele of UASMS3 were separately associated with higher feeding duration (P < 0.05). The two SNP show significant linkage disequilibrium and could also be relevant in predicting other characteristics, such as milk yield and quality in cattle. These results, however, represent the initial associations of the polymorphisms with these traits, and further efforts are required to validate these findings in other populations. [ABSTRACT FROM AUTHOR]

We report the identification and fine mapping of QTL for birth weight (BWT), preweaning ADG (PWADG), and postweaning ADG on feed (ADGF) in a commercial line of Bos taurus using an identical-by-descent haplotype sharing method. One hundred seventy-six calves of 12 bulls (9 to 30 male calves from each sire) of the Beefbooster, Inc., M1 line were typed using 71 genetic markers from bovine chromosomes (BTA) 2, 6, 14, 19, 21, and 23 (8 to 16 markers from each chromosome). Sixteen haplotypes were found to have significant (P < 0.05) associations with BWT at the comparison-wise threshold. The 16 haplotypes span 13 chromosomal regions, two on BTA 2 (9.1 to 22.5 cM and 95.0 to 100.3 cM), three on BTA 6 (8.2 to 11.8 cM, 35.5 to 49.7 cM, and 83.0 to 86.2 cM), three on BTA 14 (26.0 to 26.7 cM, 36.2 to 46.2 cM, and 52.0 to 67.7 cM), one on BTA 19 (52.0 to 52.7 cM), two on BTA 21 (9.9 to 20.4 cM and 28.2 to 46.1 cM), and two on BTA 23 (23.9 to 36.0 cM and 45.1 to 50.9 cM). Thirteen haplotypes spanning seven chromosomal regions significantly affected (P < 0.05) PWADG at the comparison-wise threshold. The seven chromosomal regions include two regions on BTA 6 (11.8 to 44.2 cM and 83.0 to 86.2 cM), one on BTA 14 (26.7 to 50.8 cM), one on BTA 19 (4.8 to 15.9 cM), one on BTA 21 (9.9 to 20.4 cM), and two on BTA 23 (17.3 to 36.0 cM and 45.1 to 50.9 cM). For ADGF, 11 haplotypes were identified to have significant associations (P < 0.05) at the comparison-wise threshold. The 11 haplotypes represented eight chromosomal regions, one on BTA 2 (9.1 to 22.5 cM), two on BTA 6 (49.7 to 50.1 cM and 59.6 to 63.6 cM), two on BTA 14 (17.0 to 24.0 cM and 36.2 to 46.2 cM), two on BTA 19 (52.0 to 52.7 cM and 65.1 to 65.7 cM), and one on BTA 21 (46.1 to 53.1 cM). The QTL regions identified and fine mapped in this study will provide a reference for future positional candidate gene research and marker-assisted selection of various growth traits. [ABSTRACT FROM AUTHOR]