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Direct and Correlated Response to Yearling Weight Selection in Hereford Cattle Using Nationally Evaluated Sires¹

The University of Georgia, Athens 30602

Abstract

Records on 726 progeny were collected in a 6-yr (1978 to 1983) Hereford cattle selection study. The selection practiced utilized top AI sires based on expected progeny difference for yearling weight from the Hereford National Sire Evaluation Program. A control line utilizing repeat matings was used to monitor environmental changes. The genetic trend in yearling weight was 5.5 ± .9 kg/yr for all progeny, and 6.2 ± .7 kg/yr with clean-up-sired progeny omitted from the analysis. Indirect change in weaning weight due to the selection for yearling weight amounted to 4.6 ± .7 kg/yr for all progeny and 5.0 ± .6 kg/yr with clean-up-sired progeny omitted. There was also an increase (P<.05) in yearling hip height (.74 ± .21 cm/yr for all progeny and .75 ± .22 cm/yr for clean-up-sired progeny omitted). A nonsignificant trend for postweaning average daily gain (7 ± 4 and 9 ± 4 g/d per yr) was also observed. No changes were found in yearling fat thickness probe. Reproductive traits measured (birth weight, calving difficulty, percentage of live calves within 24 hr of birth, pelvic area and scrotal circumference) showed no significant correlated response to yearling weight selection.

¹ This study was partially funded by the Georgia Agr. Exp. Sta. and is part of a State Project, S-3-387.

² This paper represents part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Master of Science degree in Animal Science.

³ Anim. and Dairy Sci. Dept.

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