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The Effect of Antibiotics on the Fertility of Bull Semen and their Relationship to the Estrous Cycle Length of Dairy Cattle Following Artificial Insemination¹

Kentucky Agricultural Experiment Station, Lexington, and Marshall C. Carpenter, Manager, Kentucky Artificial Breeding: Association

ABSTRACT

Fertility data were obtained for 184 semen samples collected from 25 bulls. Each sample was split into two equal portions; one portion was used as a control and the other was treated with 1,000 units each of penicillin and streptomycin per milliliter. Of 5,241 cows bred with control semen, 68.4 per cent did not return for second service within 120 to 150 days, while of the 5,299 cows bred with treated semen, 68.1 per cent apparently conceived. The fertility of the bulls ranged from 48.8 to 83.3 per cent. The addition of penicillin and streptomycin to the semen of these bulls did not significantly affect their fertility. The trend, though not statistically significant, was for the antibiotics to improve the low fertility bulls and lower the bulls ranking high in fertility.

Most of the semen was 24 to 36 hr. old during its first day of use. There was a decrease of 5.4 percentage units between the first and second day of use for the control semen and 5.0 percentage units for the treated semen. The antibiotics did not reduce this decline to a significant degree.

Among 3,321 cows which did return for second service, the mean interval between first and second service was 34.7 days. However, the modal interval was 21 days. There were highly significant differences between the distribution of returns for cows bred with control semen and for cows bred with treated semen. Among cows bred with semen containing antibiotics, a larger percentage of the returns were at intervals approximating the expected 3- and 6-wk. intervals, whereas among the controls there was a larger percentage of the returns in the 25- to 35-day and 49-day or over groups.

¹ The investigation reported in this paper is in connection with a project of the Kentucky-Agricultural Experiment Station and is published by permission of the director.