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<0.05). There was no effect of SP from high or low fertility bulls on fresh or frozen-thawed parameters assessed of caudal epididymal spermatozoa, or the fertilising ability of caudal epididymal spermatozoa. Seminal plasma reduced the osmotic resistance of caudal epididymal spermatozoa regardless of source form high or low fertility bull. Finally, this study sought to prolong the functional lifespan of spermatozoa in fresh egg yolk based diluent through the addition of antioxidants; l carnitine (0 to 20 mM), crocin (0 to 2 mM), α-tocopherol (0 to 1 mM), quercetin (0 to 250 µM) and catalase (0 to 500 IU). Following 4h at 39 o C incubation all catalase treated spermatozoa had greater acrosome intact populations compared to the control. When fresh semen was stored in the presence of antioxidants motility, lipid peroxidation and membrane fluidity decreased with time but there was no effect of treatment on any other the in vitro parameters assessed during the storage period. In conclusion, this thesis provides new insights into the physiological effects of sex-sorting on spermatozoa physiology.