Prolonging the time of semen deposition increases the pregnancy rates of ewes subjected to fixed time cervical insemination during the breeding season

The main limiting factor of artificial cervical insemination in ewes is the long and narrow fibrous cervical canal, which impedes the transport of spermatozoa and leads to lower pregnancy rates. The hypothesis that prolonging the time of semen deposition during ovine cervical insemination can increase pregnancy rates was investigated in this study. Estrus was synchronized in 150 multiparous Ujimqin ewes using a polyurethane intravaginal sponge impregnated with 45 mg of flurogestone acetate. The sponge was left in the vagina for 12 days followed by an injection of 330 IU of eCG at sponge removal. After the exclusion of two ewes due to sponge loss, the remaining 148 ewes were divided into the Treatment group (n = 75) and the Control group (n = 73). Each ewe was inseminated once between 56 and 60 h after the removal of sponges, using a new type of insemination device containing 0.25 ml of diluted semen. Semen was collected from eight Black Suffolk rams and all the ejaculates were pooled and diluted in ultra-high temperature-treated commercial skimmed milk. The time of semen deposition was prolonged to 60 s in the Treatment group, while ewes were given traditional insemination in the Control group. Pregnancy status was determined by transabdominal ultrasound examination 45 days after insemination. Lambing performance was calculated after all the ewes had been delivered. Significant differences were observed between the Treatment group and the Control group in terms of the pregnancy rate and the fecundity rate (73.3% and 93.3% vs 56.2% and 71.2%, p < .05 and p < .01, respectively). In conclusion, prolonging the time of semen deposition significantly increased pregnancy and fecundity rates in estrus-synchronized Ujimqin ewes subjected to fixed time cervical insemination.