To better understand growth trajectory and maturity differences between beef breeds, three models – Brody, spline, and quadratic – were fit to cow growth data, and resulting parameter estimates were evaluated for three breed categories – British, continental, and Brahman-influenced. The data were weight-age pairings from 4,721 cows from the U.S. Meat Animal Research Center Germplasm Evaluation Program. Parameters estimated were mature weight and maturing rate () from a Brody function, intercept for left and right segments and slope of the right segment of a linear spline, and (intercept; coinciding with weaning weight), (linear coefficient), and (quadratic coefficient) of a quadratic regression. Estimates of the coefficients from the fit of the quadratic regression and the spline function were both used to predict mature weight at six years old. All estimates were near 0.003 day-1. Mature weight estimates ranged from 594.4 to 746.0 kg. Direct heterotic effect of mature weight was estimated as 14.1 ( 2.8) kg. Weaning weight estimates ranged from 256.7 to 313.8 kg. From the fit of the three functions, British and Brahman-influenced breeds had similar weights at maturity while continental breeds were lightest. Conversely, at weaning, continental breeds were heaviest while British and Brahman-influenced breeds tended to be lighter and similar in weight. However, at neither maturity nor weaning did weights differ significantly among the breed categories. In future analyses, variance components will be estimated for mature weight, as well as individual breed and maternal heterotic effects. Keywords: beef cattle, mature weight, Brody curve, spline function

Madeline J Zimmermann, Larry A Kuehn, Matthew L Spangler, Mark R. Thallman, Warren M Snelling, Ronald M Lewis

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Growth and Development, , 689, 2018
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