Bullpower Delivery of adequate normal sperm to site of fertilisation

Summary

The project examined the effects of relocation on bull reproductive traits, sexual development in yearling bulls, the effect of yearling mating on pregnancy and calving rates, causes of preputial prolapse in bulls, the importance of sperm morphology as a reproductive trait and the effect of herd dispersion and bull mating percentages on pregnancy rates.

There was no effect of genotype, concentrate feeding or relocation per se, on semen traits.

Mating yearling Bos indicus bulls reduced pregnancy rates. Physical but not semen traits of yearling bulls were indicative of these traits at 2 years of age. Supplementing yearling bulls with concentrates did not affect semen traits.

Repeatability of normal sperm was high once bulls reached sexual maturity. Pregnancy rates were reduced using bulls with less than 50% normal sperm. The use of 2.5% reproductively-sound bulls appears adequate under most conditions.

Predisposition to preputial prolapse was equivocal.

Recommendations for research included further investigation on the effects of relocation; defining threshold levels for high energy diets for yearling bulls; methods to increase the proportion of yearling bulls passing a BBSE; determining heritability and genetic relationships of male reproductive traits; and researching cattle reproductive behaviour to explain differences in calf output of bulls.