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Sire Effect and Repeatability of Beef Cow Productivity¹

University of Tennessee, Knoxville 37901

Abstract

Average daily gain to weaning (WNADG) of 1,220 Angus calves from 397 dams and 544 Polled Hereford calves from 182 dams was used as a measure of cow productivity to determine the extent to which sire differences influence repeatability of WNADG, considered as a trait of the cow. Least-squares procedures were used to obtain additive constants for effects of sex of calf, age of dam and year. Estimates of intraclass correlations of successive WNADG values recorded for the same cow, adjusted to remove differences in sex of calf, age of dam and year, were .49 ± .04 and .35 ± .03 for Polled Hereford and Angus, respectively. Removal of sire-year effects from the data reduced (P<.05) the estimate of repeatability of WNADG in Angus (to .30 < .03) but not in Polled Herefords. The greater reduction in the repeatability estimate in the Angus data after removal of sire effect is logically attributable to the larger (P<.10) sire variance in the Angus data. Correlation among genes received by calves from the same sire would contribute to repeatability on a cow basis, and this contribution would be increased by a larger sire variance.

¹ Published with the approval of the Dean of the Univ. of Tennessee Agr. Exp. Sta., Knoxville 37901.

² Present address: Dept. of Anim. Sci., The Ohio State Univ., Columbus 43210.

³ Anim. Sci. Dept., Univ. of Tennessee, Knoxville 37901.