Semen quality parameters including metabolites, sperm production traits and fertility in young Norwegian Red AI bulls

Abstract

Genomic selection in cattle breeding has gradually allowed younger bulls to be recruited for semen production. In this study, sperm quality parameters, seminal plasma and sperm metabolites, semen production capacity and fertility in young Norwegian Red bulls were analysed. For in vitro analyses of sperm quality and metabolites, ejaculates were collected from the same 25 bulls at both 14 and 17 months of age. Semen production and fertility data were collected for all Norwegian Red bulls in production from December 2017 throughout 2019. Bull fertility was measured as 56 days non-return rate (NR56), for both age groups. In both fresh and frozen-thawed semen samples, the proportion of hyperactive spermatozoa, average path velocity, curvilinear velocity and amplitude of lateral head displacement were higher in samples collected at 17 months of age compared to 14 months (P<0.05). In addition, several amino acids including arginine, glutamine, cysteine and proline, were affected by age (P<0.05). The concentrations of K and Ba increased significantly (P<0.05) with age in both seminal plasma and sperm cells. Sperm concentration and volume of the ejaculate increased significantly with increasing age, while the percentage of discarded batches decreased. The bulls’ NR56 decreased significantly with increasing age (75% vs. 74%). However, the difference of 1% is unlikely to be of biological importance. In conclusion, even small age differences in young bulls may significantly affect several sperm quality parameters, metabolite levels and semen production traits.