J. Anim Sci.
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J. Anim Sci. 1984. 58:550-555.
© 1984 American Society of Animal Science
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An Evaluation of Bias in Estimated Breeding Values for Weaning Weight in August Beef Cattle Field Records. II. Estimates of Bias Due to Genetic Trend1,2,3,

W. A. Zollinger and M. K. Nielsen

University of Nebraska, Lincoln 68583-0908

Abstract

Field records (53,989) from the American Angus Association were used to evaluate the impact of bias associated with genetic trend in estimated breeding values for weaning weight. Annual estimates of breeding values were calculated using the reported weaning weight ratios and ratios adjusted for estimated genetic trend. Genetic gains were assumed to be consistently linear. Bias was estimated as the difference between the two estimates, and herd averages across years for dam's bias ranged from .38 to 3.86 ratio units. The bias was a function of the magnitude of the estimated trend and the generation interval. The impact of this bias was small in young cows, but increased rapidly after their fourth or fifth calves. When annual genetic trend was less than .75 ratio units, the loss in selection response (based upon selecting the top 10 and 50% of males and females, respectively) did not exceed 2.5%. In herds with trends between .75 and 1.1 units/yr, the loss was 6 to 8%. In the five herds where estimated trend exceeded 1.1 units/yr, the loss ranged from 10.8 to 25.2%.

Footnotes

1 Published as Paper No. 6986 Journal Series, Nebraska Agr. Exp. Sta., Lincoln and a contribution from Regional Project NC-1, Improvement of Beef Cattle Through Breeding Methods.

2 Appreciation is expressed to the Amer. Angus Assoc, and fifteen cooperating breeders for providing data used in this study.

3 Anim. Sci. Dept.






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