Influence of insemination time on the fertility of sex sorted frozen-thawed Y-sperm in red deer.

The aim of this study was to assess the effect of insemination timing on pregnancy rates in red deer (Cervus elaphus) when using sex-sorted sperm samples. Semen was collected by electroejaculation from 8 mature stags and processed to obtain: Conventional samples, following standard freezing procedures for commercial purposes; Control sorted samples, diluted and handled as per sorted samples but without being submitted to the sorter passage; and Y Sex Sorted (YSS) samples. Hinds were synchronized via intravaginal CIDR (Controlled Internal Drug Release) placement and given eCG (Folligon PMSG Serum Gonadotrophin) on day 12, upon CIDR removal. They were then inseminated with one of each sperm treatment, at the following post-eCG intervals: I_1, 55:01-55:30 h; I_2, 55:31-56:00 h; I_3, 56:01-56:30 h; or, I_4, 56:31-57:00 h. Pregnancy rates were assessed at parturition. Average pregnancy rates were highest (P < 0.05) for Conventional samples (77.6%), but similar between YSS (49.8%) and Control sorted (51.3%) samples. However, when insemination interval was taken into account, pregnancy rates within the YSS group, pregnancy rates were 80 and 83.1% for I_1 and I_2, respectively were obtained. Notably, these rates were similar (P > 0.05) to the average pregnancy rates obtained with Conventional samples (77.6%). As expected, YSS sperm yielded 94% male offspring contrasting with the 57% males obtained with Conventional and Control sorted samples. Our findings support the importance of developing specific insemination timing protocols to improve pregnancy rates when using frozen-thawed sex-sorted sperm. These findings provide the foundation for further investigations in order to determine why the YSS sperm are able to fertilize the oocyte in a shorter period of time than the conventional samples.