J. Anim Sci.
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J. Anim Sci. 1987. 64:357-365.
© 1987 American Society of Animal Science
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Expected Responses to Index Selection for Direct and Maternal Additive Effects of Gestation Length or Birth Date in Beef Cattle1

Sara Melin Azzam and M. K. Nielsen2

University of Nebraska, Lincoln 68583-0908

Abstract

Response to selection for earlier birth date or shorter gestation length was studied by a deterministic simulation model. Phenotypic variances, additive direct and maternal variances and additive direct by maternal covariances were varied based on literature estimates. An index that maximizes the sum of the direct and maternal breeding value was used as the selection criterion. The index utilized information on paternal and maternal half sibs as well as on progeny. The amount of information in the index was also varied. Males were always mated to produce 25 viable progeny per generation. Maximum response was achieved when males were selected on an index including information on their own record, 50 paternal half-sibs, three maternal half-sibs and 0 or 25 progeny. Females were selected on an index that differed only in the number of progeny (two instead of 0 or 25) included in the index. Under these assumptions, the maximum annual response to selection on birth date was .76 d and to selection on gestation length, .6 to 2.1 d, depending on the assumed population parameters. The correlated response in direct breeding value was positive, while that in maternal breeding value was negative. The economic feasibility of selecting for either gestation length or birth date would depend upon management objectives and the cost of recording breeding dates in addition to birth dates.

Footnotes

1 Published as Paper No. 8056, Journal Series, Nebraska Agr. Res. Div., Lincoln.

2 Anim. Sci. Dept., Univ. of Nebraska, Lincoln 68583-0908.






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Copyright © 1987 by the American Society of Animal Science.