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Heritabilities of Predicted Performance Measures in Beef Bull Tests and Their Relationships with Feedlot Efficiency Measures¹

University of Guelph, Guelph, Ontario, Canada

Abstract

Indices developed from performance test data [weight at market finish , days to market finish , rate of economic maturing and relative growth rate ] were assessed for associations with feedlot phase gross margin (GM), gross margin per day (GMPD) and feed conversion from initial to market weights (FC) at three levels of feed cost and two rates of interest. Heritabilities of indices were estimated from the pooled within-breed regressions of 105 sons on 51 sires. The indices and were positively correlated with GM at low feed cost and negatively correlated at high feed cost, while associations with GMPD were negative at all levels of feed cost and rates of interest. For and , correlations with GMPD were strongly positive at all times; correlations with GM changed from strongly positive to negative as feed cost fell. Only and were highly associated with FC. Days to market, when adjusted to a constant initial proportion of market weight , was highly heritable (.90 ± .48) while and were moderately so (.56 ± .29 and .46 ± .24). Selection of station-tested breeding stock primarily for is suggested by its heritability and association with efficiency. Within its range of acceptability to the industry, WM will be favored or discounted dependent on short-term economics and availability of feeder cattle.

¹ The statistical assistance of O. B. Allen, technical assistance of C. Watson, A. McBurney, C. Haworth and M. McMorris and the financial assistance of the Ontario Cattlemen's Assoc, and Ontario Ministry of Agriculture and Food are gratefully acknowledged.

² Dept. of Med. Biochem., Univ. of Calgary, 3330 Hospital Drive N.W., Calgary, Alberta, Canada, T2N 1N4.

³ Dept. of Anim. and Poult. Sci., Univ. of Guelph, Guelph, Ontario, Canada, N1G 2W1.