Quality and Freezability of Semen from Growing and Aged Dairy Bulls

Abstract

Five groups of nine to ten Holstein bulls, over the age range from one and a half to six years, and a sixth group of 15 aged Holstein bulls were ejaculated four times per week for four weeks following an initial adjustment period. Sperm output in the aged bulls (72 to 150 months old) was considerably lower than in the groups ranging in age from 34 to 69 months. The percentage of morphologically normal sperm in semen at the time of collection and of motile sperm after freezing in pellets and ampules was lowest in the aged bulls. Nonreturn data available for this group indicated that the per cent unstained before freezing and the per cent normal and per cent motile sperm after freezing were significantly correlated with fertility (P<.01). Since semen quality was highest in bulls not yet old enough to complete the progeny test, freezing and storing selected semen samples from these bulls may be desirable. Semen quality of the youngest group was highly correlated with tests conducted a year later. If this relationship persists for several years, some young bulls with inferior semen quality might effectively be culled before being sampled in progeny test programs.