Optimising the use of fresh semen: insights for use with young genomically-selected bulls

With the advent of genomic selection, bulls are being used in the artificial insemination industry during early puberty. These young bulls produce ejaculates of low volume and low spermatozoa concentration that are highly valued. The objective of this thesis was to investigate methods that best utilise the semen from young genomically-selected bulls. As a result of the characterisation of in vitro quality of sex-sorted (SS) and non-sex-sorted (NS) fresh and frozen spermatozoa there was ~40% of the SS fresh spermatozoa agglutinated while the SS (fresh and frozen) had lower levels of oxidative stress. Both motility and viability positively correlated to field fertility of SS spermatozoa, however, no functional assessments correlated to field fertility of NS spermatozoa. Different seminal plasma (SP) components were correlated to field fertility for both SS and NS cohorts. The effect of seminal plasma from high and low fertility bulls on the function of caudal epididymal spermatozoa was investigated via a number of in vitro assessments. Results from these assessment demonstrated a beneficial effect of SP on the motility of caudal epididymal spermatozoa (P