Breed and heterotic effects for mature weight in beef cattle

Authors: ZIMMERMANN, MADELINE - University Of Nebraska; Kuehn, Larry; SPANGLER, MATTHEW - University Of Nebraska; Thallman, Richard - Mark; Snelling, Warren; LEWIS, RONALD - University Of Nebraska

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2021
Publication Date: 7/14/2021
Citation: Zimmermann, M.J., Kuehn, L.A., Spangler, M.L., Thallman, R.M., Snelling, W.M., Lewis, R.M. 2021. Breed and heterotic effects for mature weight in beef cattle. Journal of Animal Science. 99(8). Article skab209. https://doi.org/10.1093/jas/skab209.
DOI: https://doi.org/10.1093/jas/skab209

Interpretive Summary: Mature cow weight is a driver of cost and efficiency in commercial cattle breeding, primarily due to increased feed requirements. While some production systems can accommodate larger cows, having tools to manage cow weight would be helpful in reducing costs for commercial cattle operations. Our objective was to estimate current breed differences for mature weight from sixteen different breeds using data from the U.S. Meat Animal Research Center Germplasm Evaluation Program, where cows were daughter or granddaughters of influential industry bulls. Mature weight was predicted for all cows at 6 years of age and used to determine breed differences for mature weight. Breed differences were adjusted for industry sampling using bull yearling weight EPDs. Resulting breed differences can be used to inform breeding programs where limiting cow size could increase efficiency and thus overall profitability.

Technical Abstract: Cow mature weight (MWT) is heritable and affects the costs and efficiency of a breeding operation. Cow weight is also influenced by the environment, and the relationship between the size and profitability of a cow varies depending on production system. Producers, therefore, need tools to incorporate MWT in their selection of cattle breeds and herd replacements. The objective of this study was to estimate breed and heterotic effects for MWT using weight-age data on crossbred cows. Cow’s MWT at 6 yr was predicted from the estimated parameter values—asymptotic weight and maturation constant (k)—from the fit of the Brody function to their individual data. Values were obtained for 5,156 crossbred cows from the U.S. Meat Animal Research Center (USMARC) Germplasm Evaluation Program using 108,957 weight records collected from approximately weaning up to 6 yr of age. The cows were produced from crosses among 18 beef breeds. A bivariate animal model was fitted to the MWT and k obtained for each cow. The fixed effects were birth year-season contemporary group and covariates of direct and maternal breed fractions, direct and maternal heterosis, and age at final weighing. The random effects were direct additive and residual. A maternal additive random effect was also fitted for k. In a separate analysis from that used to estimate breed effects and (co)variances, cow MWT was regressed on sire yearling weight (YWT) Expected Progeny Differences by its addition as a covariate to the animal model fitted for MWT. That regression coefficient was then used to adjust breed solutions for sire selection in the USMARC herd. Direct heterosis was 15.3 ± 2.6 kg for MWT and 0.000118 ± 0.000029 d-1 for k. Maternal heterosis was -5.7 ± 3.0 kg for MWT and 0.000130 ± 0.000035 d-1 for k. Direct additive heritabilities were 0.56 ± 0.03 for MWT and 0.23 ± 0.03 for k. The maternal additive heritability for k was 0.11 ± 0.02. The direct additive correlation between MWT and k was negligible (0.08 ± 0.09). Adjusted for sire sampling, Angus was heaviest at maturity of the breeds compared. Deviations from Angus ranged from -8.9 kg (Charolais) to -136.7 kg (Braunvieh). Ordered by decreasing MWT, the breeds ranked Angus, Charolais, Hereford, Brahman, Salers, Santa Gertrudis, Simmental, Maine Anjou, Limousin, Red Angus, Brangus, Chiangus, Shorthorn, Gelbvieh, Beefmaster, and Braunvieh. These breed effects for MWT can inform breeding programs where cow size is considered a key component of the overall profitability.