Postpuberal changes in semen production of Charolais bulls ejaculated at high frequency and the relation between testicular measurements and sperm output.

Twelve Charolais bulls were ejaculated once weekly (1• and 10 bulls six times weekly (6• from puberty to 2 years of age to determine the effect of age and ejaculation frequency on semen characteristics, sperm output and testes growth; 6• 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 6• bulls increased 2.4 times from 14.0 • 109 at 53 to 56 weeks to 33.6 • 109 at 101 to 104 weeks of age and for 1• bulls increased 2.2 times from 5.0 • 109 to 11.2 • 109 at the same ages. For 6• as compared to 1• bulls, ejaculate volume was smaller (P<.O1) but total sperm and total motile sperm per week were greater (P<.O1); 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