The effect of dilution rate and successive semen collections on sperm quality and sexual motivation of sexually mature South African Merino rams.

This study investigated whether dilution rate and successive semen collections influenced sperm viability, morphology, motility and male sexual motivation in sexually mature South African Merino rams (SAMR). Semen was collected from 11 rams up to either sperm or behavioural exhaustion. Semen was then immediately serial diluted to make 0, 2, 4, 8 and 16× dilutions with Hams F10 diluent. Following dilution, sperm motility was evaluated using computer-assisted sperm analysis (SCA®), while sperm morphology and viability were assessed using nigrosin-eosin staining and SYBR14/PI, respectively. Male sexual motivation was recorded by reaction time to first mount, while male dexterity was calculated as the ratio of mounts to ejaculations. An increase of dilution rate did not affect sperm motility (P > 0.05) but resulted in a significant decrease in the percentage of live normal sperm (P < 0.05). Furthermore, while sperm concentration and number decreased with semen collection number (P < 0.05), no effect was detected on sperm viability, morphology and motility (P > 0.05), except for average curvilinear velocity which showed a biphasic trend (P < 0.05). Mating success and reaction time were negatively affected by successive semen collections (P < 0.05), while male dexterity was unaffected (P > 0.05). Nevertheless, relatively high numbers of motile sperm (>2 billion) were collected up to the 4th successive semen collection, with a short initial reaction period (<25 s) and good success rate (>65%). SAMR thus withstood frequent semen collections without affecting their sperm reserves or sexual motivation. Further studies are required to investigate optimal conditions for semen collection and artificial insemination in this breed.