Bovine sperm abnormalities: prevalence, etiology and mechanisms leading to infertility

Abstract

Sperm morphology is an excellent predictor of the outcome of natural mating1,2 and artificial insemination (AI),3,4 and success of in vitro fertilization5 in animals and humans. Bovine sperm abnormalities are classified based on origin (primary, secondary or tertiary), effect on fertility (major vs minor), location of the sperm defect (head, midpiece, or tail), or whether its effects on fertility can be ameliorated by increasing the number of sperm in the inseminate (compensable vs uncompensable).6 Although prevalence of various types of sperm abnormalities is low in the ejaculates and ~ 83% of bulls subjected to a traditional breeding soundness examination are classified as satisfactory breeders exclusively based on sperm morphology, it is noteworthy that 17% of bulls subjected to breeding soundness evaluation were designated unsatisfactory solely on the basis of sperm morphology, highlighting its importance in Alberta.7 Although an association between sperm abnormalities and infertility has been established and functional impairments of sperm abnormalities have been documented,8 the molecular basis of impaired function of abnormal sperm remains unknown. Our recent studies demonstrated that expression of sperm proteins are altered in abnormal sperm, thereby affecting fertility. Since sperm DNA is transcriptionally inactive, content of sperm proteins in the mature sperm influences fertilizing ability. This paper summarizes current knowledge regarding the prevalence, etiology and mechanisms of infertility due to abnormal bovine sperm.