Studies on the number of ewes joined per ram for flock matings under paddock conditions. II. The effect of mating on semen characteristics

Abstract

Semen characteristics were studied prior to and during the paddock joining of rams to varying numbers of ewes in a series of three experiments.

A marked fall in ejaculate volume, sperm density, and their product, total number of sperm per ejaculate to levels of c. 0.3 ml, 1.5 x l0⁹ sperm/ml, and 0.45 x l0⁹ total sperm respectively occurred during the first 4 days of joining. Although there were large differences in the number of ewes joined per ram (25 to 100) and consequently the number of ewes served per ram per day, the depression in these semen characteristics occurred to a similar extent in all rams during the first 2 weeks of mating. By examining the data for all collections throughout the joining period, however, highly significant negative correlations were obtained for ejaculate volume, sperm density, and total number of sperm per ejaculate in each case with the number of ewes served during the 4 days preceding semen collection. Increases in the proportion of abnormal sperm were found sporadically in the ejaculates of rams during joining.

Rams 2½ years old produced significantly more sperm per ejaculate before, during, and after the 6 week joining period than rams 1½ years old.