FACTORS AFFECTING PRESERVATION AND FERTILITY OF BULL SPERM - A BRIEF REVIEW

This paper is a brief review of the factors that determine the number of sperm required for insemination to obtain high fertility and ways t hat sperm viability might be prolonged. Damage to sperm during freezin g results in a requirement, after thawing, of about 6x10(6) motile spe rm (>10x10(6) total) per insemination to achieve near-maximal fertilit y, whereas 2.5x10(6) motile fresh sperm result in high nonreturn rates . Multiple inseminations to bracket the time of ovulation are usually not economical except in superovulated cows. Earlier unpublished work on sperm packaging for slow release in the cow and methods for stabili zing membranes to increase sperm survival time in the cow are discusse d.Current studies are directed towards reducing catabolic metabolism o f sperm and studying membrane changes during freezing and thawing and during incubation with bovine oviduct epithelial cells. Studies with b ull sperm indicate that the choline and ethanolamine phosphoglyceride components of their membranes represent an unstable configuration. Exp osure of sperm to liposomes with the sterol cholesterol can alter the phospholipid bilayer and increase capacitation time. Similar approache s may produce sperm with a longer fertilizing life following inseminat ion. New procedures in vitro permit low cost modelling of fertilizatio n, which will facilitate research by reducing the cost of studies in v ivo.