Post-thaw semen quality in young bull ejaculates before being accepted for commercial semen doses.

Abstract

Genomic selection enables bulls with desirable characteristics to be identified at a young age, but sperm quality can be poor in the ejaculates of young bulls. Few studies have been done on post-thaw sperm quality in bulls less than 10 months old. The objective of this study was to determine the age at which post-thaw sperm quality was acceptable for artificial insemination. Semen was collected by artificial vagina; samples containing 100-500 million spermatozoa/ml were frozen for this study. Post-thaw analyses of membrane integrity (MI), mitochondrial membrane potential (MMP), chromatin integrity, morphology, production of reactive oxygen species and sperm kinematics were made. The age at which ejaculates exceeded the breeding company's thresholds of acceptance varied considerably among individuals, with 285 days being the earliest. Morphology (p<0.003), MI (p=0.0096), high MMP (p=0.043) and superoxide production (p=0.0084) increased between the first and last ejaculates but reached acceptable levels at different ages for individual bulls. It was possible to obtain acceptable post-thaw sperm quality from samples even though sperm concentration was lower than the breeding company's threshold. Therefore, it might be feasible to use ejaculates earlier than is currently considered possible, by modifying semen handling protocols.