This study was undertaken to investigate the effects of time from CIDR withdrawal and ewe age on conception rates in a sheep artificial insemination programme. Four groups each of 50 Romney ewes (balanced for ewe age, two-tooths vs mixed age) were synchronised by intravaginal insertion of CIDRs for 11 days. Ewes in each group were inseminated at 36h, 42h, 48h or 54h respectively from CIDR withdrawal by cervical insemination using 200 million sperm per insemination of fresh semen. Conception was determined by measuring non-return rates using harnessed rams. Conception rates increased (P<0.10) with the interval between CIDR withdrawal and fixed time insemination thus: 36h, 37%; 42h, 49%; 48h, 59%; and 54h, 60%. Conception rates were greater in mixed age ewes (58%) than in two tooth ewes (43%) (P<0.05). There was no interaction between the effects of age and time of insemination relative to CIDR withdrawal. It is concluded that there may be advantages in extending the interval between CIDR withdrawal and insemination to 48 to 54 h as opposed to the current industry recommendations of 45 to 48 hours.

TG, Watson, BC Hosking, and PF McKee

Proceedings of the New Zealand Society of Animal Production, Volume 53, , 239-242, 1993
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