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Reproductive Capacity of Beef Bulls. III. Postpuberal Changes in Fertility and Sperm Morphology at Different Ejaculation Frequencies^{1, 2, 3,}

The Pennsylvania State University⁴, University Park

Abstract

Changes in fertility and proportion of morphologically normal sperm were determined from puberty to 2 yr. of age on eight Angus and nine Hereford bulls ejaculated at three different frequencies.

Fertility of beef bulls, based on 60- to 90-day nonreturn rates for 714 semen samples and 27,912 first services, increased (P<.05) between 1 and 2 yr. of age and varied (P<.01) among bulls within breed-frequency groups. Fertility was not significantly affected by ejaculation frequency or breed. Mean nonreturn rates improved (P<.05) from 68% for 53 to 72 wk. to 74% for 73 to 88 wk. of age, but remained at 73% for 89 to 104 wk. of age. Although not included in the analysis, a nonreturn rate of 69% was obtained on 1,017 additional first services to 10 of 17 bulls which yielded usable ampules before 1 yr. of age.

The percentages of normal sperm were not influenced by ejaculation frequency or breed, but varied (P<.01) among bulls within breed-frequency groups. Analysis of variance also showed that the percentages of normal sperm increased (P<.05) with age. Although the data suggested a relationship between morphology and fertility, analysis of covariance showed them to be unrelated.

In conclusion, these data demonstrate that progeny testing of beef bulls can be initiated at puberty since fertility is sufficiently high to provide an adequate calf crop.

¹ Authorized for publication as Paper No. 3446 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park.

² Supported in part by The Pennsylvania Association of Animal Breeders and the Linde Company, Division of Union Carbide Corp.

³ Appreciation is expressed to Amber R. Keene, D. C. Cunningham and R. E. Pearson for technical assistance and to the personnel of Atlantic Breeders Cooperative, Lancaster, Pa., and Northeastern Breeders Association, Tunkhannock, Pa., for their assistance and cooperation.

⁴ Dairy Breeding Research Center, Department of Dairy Science.