F. S. Schenkel

Genetic parameters and breed differences for feed efficiency, growth, and body composition traits of young beef bulls

Genetic associations between feed efficiency, growth, and live ultrasound measured body composition traits were studied in purebred beef bulls of six breeds in Ontario bull test stations from 1991 to 2000. Feed traits included average daily feed intake (FI), feed conversion ratio (FCR), and residual feed intake [feed intake adjusted for production alone (RFIp) or production and backfat thickness (RFIb)]. Growth traits were average daily weight gain (ADG), mid-test metabolic weight (MW), hip height (HH), and scrotal circumference (SC). Body composition traits included ultrasound backfat thickness (BF), longissimus muscle area (LMA), and predicted percentage of intramuscular fat (IFAT). Bulls were measured every 28 d for weight and individual feed intake, and at the end of test for ultrasound body composition traits. Number of records per trait ranged from 2284 (FI) to 13 319 (ADG). Fixed effects of test group, breed and end of test age (within breed), and random effects of animal and herd of origin were mo...

Comparison between estimation of breeding values and fixed effects using Bayesian and empirical BLUP estimation under selection on parents and missing pedigree information

Bayesian (via Gibbs sampling) and empirical BLUP (EBLUP) estimation of fixed effects and breeding values were compared by simulation. Combinations of two simulation models (with or without effect of contemporary group (CG)), three selection schemes (random, phenotypic and BLUP selection), two levels of heritability (0.20 and 0.50) and two levels of pedigree information (0% and 15% randomly missing) were considered. Populations consisted of 450 animals spread over six discrete generations. An infinitesimal additive genetic animal model was assumed while simulating data. EBLUP and Bayesian estimates of CG effects and breeding values were, in all situations, essentially the same with respect to Spearmans rank correlation between true and estimated values. Bias and mean square error (MSE) of EBLUP and Bayesian estimates of CG effects and breeding values showed the same pattern over the range of simulated scenarios. Methods were not biased by phenotypic and BLUP selection when pedigree information was complete, albeit MSE of estimated breeding values increased for situations where CG effects were present. Estimation of breeding values by Bayesian and EBLUP was similarly affected by joint effect of phenotypic or BLUP selection and randomly missing pedigree information. For both methods, bias and MSE of estimated breeding values and CG effects substantially increased across generations.

Degree of connectedness among groups of centrally tested beef bulls

The degree of connectedness among test groups (TG) of bulls tested in central evaluation stations from 1988 to 2000 in Ontario, Canada, was evaluated using the following methods: average prediction error variance of the difference between estimated breeding values (PEVD), variance of estimated differences between test group effects (VED), connectedness rating (CR), and total number of direct genetic links between test groups (GLT). The model used in the analysis included the effects of breed and TG (fixed) and animal (random). PEVD was assumed the most adequate measure of connectedness and results from the alternative methods VED, CR, and GLT were compared against it. Models to predict the average PEVD of pairs of TG and the average PEVD of each TG with all other TG on the basis of VED, CR, and GLT were developed. Results from all measures of connectedness indicated an unfavorable trend in the degree of connectedness after 1994. The average PEVD of pairs of TG can be better predicted on the basis of the m...

Herd of origin effect on weight gain of station-tested beef bulls

The effect of herd of origin on genetic evaluation of weight gain of beef bulls in central test stations was examined by univariate and bivariate analyses, which included bull’s estimated weight gain on test (BEG) and pre-weaning gain (WG) of bulls and their contemporaries in the herd of origin. Bulls were weighed every 28 days on 112 or 140-day station test. BEG was estimated fitting fixed linear regressions to the weights on test of each bull. The bivariate model included random direct additive genetic and dam effects and fixed breed effects for both traits, fixed management group and sex of calf by age of cow effects for WG and fixed test group and random herd of origin by year (HY) effects for BEG. Variance components and EBV were estimated applying models with or without HY effect, which were compared using likelihood ratio test and two information criteria. The effect of HY was significant on BEG, contributing around 8% to total phenotypic variation. Inclusion of HYeffect caused EBV to re-rank among top bulls (rank correlation of 0.85 and 0.75 among 5% and 1% best bulls, respectively). Interaction of HY by sire was shown not to be of concern. D 2003 Elsevier B.V. All rights reserved.

Comparison of models and impact of missing records on genetic evaluation of calving ease in a simulated beef cattle population

This study compared the application of a bivariate linear-linear (LL) and a linear-threshold (LT) sire-maternal grandsire model for genetic evaluation of calving ease (CE), using birth weight (BW) as a correlated trait, and assessed the impact of missing records on genetic evaluation of CE in a simulated multi-breed beef population that mimicked phenotypic and genetic parameters of beef cattle in Ontario. Models included fixed age-of-dam by sex-of-calf, management group, breed and heterosis effects, and random direct and maternal genetic, maternal permanent environment and residual effects. The LL model was applied to BW and CE Snell scores, and LT model was applied to BW and CE raw scores. CE evaluations were similar between the LL and LT models with no obvious advantage for either model. The two models performed similarly with respect to accuracy and rank correlation of predicted genetic effects and recovered true values of genetic parameters and fixed effects, except for CE maternal heterosis from LL m...