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Genotype X Environment Interactions in Beef Sire Evaluation:^{1, 2,} The Importance of Sire by Year Interactions for Postweaning Traits³

University of Missouri, Columbia 65201

Abstract

Data on postweaning traits of 876 (411 and 465 ) yearlings born to 17 sires during the period 1961 through the 1967 calving seasons for the registered Hereford herd at Weldon Springs, Missouri, were available for analysis to estimate the importance and magnitude of the sire X; year interaction effects. The traits considered for analysis were: (a) average daily gain in feedlot (A.D. G.F.) of the bull calves; (b) average daily gain on pasture (A.D.G.W.P.) of the heifers; (c) 392-day weights of bull calves; (d) 550-day weights of heifers; and (e) yearling conformation scores at the end of full feeding and pasture seasons, respectively, for the bull and the heifer calves.

The results from this study were different for bulls and heifers. In bull calves, the sire x; year interaction effects were significant and of important magnitude for yearling weight but indicated only a possibility of importance for yearling scores. In the heifers, however, these interaction effects were unimportant and nonsignificant for both traits. The differences in the results observed between the bull and the heifer calves were attributed not to the age at which the measurements were taken, but to the differences in the feeding conditions and sex hormones. Bulls were full fed for a 140-day period following weaning, whereas, heifers were limited fed during the winter and pastured during the next summer. Therefore, it is suggested that experiments be conducted where both bull and heifer calves were full fed for a 140-day period after weaning, and if no sire x; sex interaction is found, this would suggest that a sire could be evaluated on the basis of 1 year's data on his heifer calves under prevailing beef production practices.

Finally, coefficients of correlation between ²_SY and ²_S, and ²_SY and RS₁S₂ (genetic relationship between sires) were estimated to determine if a relationship between genetic width (genetic diversity of sires) and magnitude of interaction effects existed. Except for 392-day weight in the bull calves for the former type and for yearling score in the heifers for the latter type, they were not significant.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 6358. Approved by the Director.

² Department of Animal Husbandry.

³ A part of a Ph.D. thesis submitted by S. N. Pani.

⁴ Present address: Department of Animal Husbandry, Orissa University of Agriculture and Technology, Bhubaneswar-3, Orissa, India.