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Postpuberal Changes in Semen Production of Charolais Bulls Ejaculated at High Frequency and the Relation between Testicular Measurements and Sperm Output^{1, 2,}

The Pennsylvania State University^,5, University Park 16802

Abstract

Twelve Charolais bulls were ejaculated once weekly (1x) and 10 bulls six times weekly (6x) from puberty to 2 years of age to determine the effect of age and ejaculation frequency on semen characteristics, sperm output and testes growth; 6x weekly sperm output at 2 and 3 years of age was determined for each of the 22 bulls. Significant increases as bulls aged were found in sperm concentration, sperm motility, weekly total sperm and total motile sperm output, scrotal circumference and width (P<.01) and ejaculate volume (P<.05). From 1 to 2 years of age, average weekly sperm output for 6x bulls increased 2.4 times from 14.0 x 10⁹ at 53 to 56 weeks to 33.6 x 10⁹ at 101 to 104 weeks of age and for 1x bulls increased 2.2 times from 5.0 x 10⁹ to 11.2 x 10⁹ at the same ages. For 6x as compared to 1x bulls, ejaculate volume was smaller (P<.01) but total sperm and total motile sperm per week were greater (P<.01); differences for sperm motility, sperm concentration and scrotal circumference and width were not significant.

Scrotal circumference and width each increased by 32% from puberty (41 ± 1 weeks) to 2 years of age with slightly over three-fourths of the increase occurring between puberty and 65 weeks of age. Scrotal circumference at 1 and 1.5 years of age was correlated .44 and .52 (P<.05) with 6x weekly sperm output at 2 years of age and .62 and .75 (P<.01) with 6x weekly sperm output at 3 years of age. Testes growth rate, based on the percentage increase in scrotal circumference between 1 and 1.5 years of age, was not significantly correlated (.30) with 6x weekly sperm output at 3 years of age. The correlation increased to .61 (P<.01) when testes growth rate during the first 24 weeks after puberty was used. Thus these relationships accounted for up to 56% of the variation in sperm output. These results and other evidence discussed support the postulate that, except for early detection of bulls with a potential for severe testicular underdevelopment, scrotal measurements of young bulls cannot be used to predict subsequent sperm output precisely.

¹ Authorized for publication as Paper No. 4881 in the Journal Series of The Pennsylvania Agricultural Experiment Station, University Park, on June 12, 1975.

² Supported in part by Atlantic Breeders Cooperative, Lancaster, Pa., Northeastern Breeders Association and Sire Power, Inc., Tunkhannock, Pa., and the American-International Charolais Association, Houston, Texas.

³ Present address: Atlantic Breeders Cooperative, 1575 Apollo Drive, Lancaster, PA 17601.

⁴ Appreciation is expressed to Mrs. A. Keene, Mrs. H. Homan, Mrs. T. Shirk and Mr. M. Holsopple for their assistance.

⁵ Dairy Breeding Research Center, Department of Dairy and Animal Science.