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Effect of Inbreeding on the Estimated Breeding Soundness of Yearling Hereford Bulls

Colorado State University^,2, Fort Collins

Abstract

A study on 311 yearling Hereford bulls showed that inbreds were inferior to linecrosses in estimated breeding soundness. A comparison of the bulls' overall classification as satisfactory, questionable or unsatisfactory prospective breeders showed a statistically significant difference between inbred and linecross bulls, but a non-significant difference between inbred and cooperators' outbred bulls.

Differences in physical suitability for breeding of inbred, linecross and outbred bulls were not statistically significant. An analysis of the sources of variation for individual semen characteristics indicated highly significant differences from year to year for morphology and percent sperm alive and a significant difference between mating systems for sperm morphology. Inbreeding intensity within the limits of these data did not appear definitely to account for increased infertility among the inbreds. There was however, some suggestion of a retarding effect of inbreeding on sexual maturity. The data further suggested that lower fertility may be due to characteristic infertility in a few lines rather than among all inbreds.

¹ The authors wish to acknowledge the assistance of Drs. F. Scott and E. J. Carroll, Veterinarians, and Kent Riddle, Assistant Animal Husbandman.

² Approved for publication as scientific paper SS-590 of Colorado Agricultural Experiment Station. It is included in the Western Section Project W-1 in cooperation with the A.P.H. Branch, U.S.D.A.

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