Low sperm numbers and ambient temperature storage are two important factors in the successful AI system for dairy cattle in New Zealand. Similar technologies with ram semen are required before the establishment of a similar AI system within the NZ sheep industry is feasible. A trial involving a total of 1200 Romney ewes was conducted in April 1997 to examine the effects of inseminate dose (50, 25, or 5 x 106 sperm) of semen held for up to 9 h at 20°C in two diluents (RSD-1 and Tris + egg yolk). In the first half of the trial ewes were laparoscopically inseminated with semen from Finn rams at set times (49 and 56 h) after CIDR removal, while in the second half of the trial ewes were inseminated with semen from Romney rams following the detection of oestrus, after CIDR removal, resulting in insemination times of 26, 44 and 49 h post removal. Returns to service in the cycle following AI were recorded and ewes were scanned for pregnancy 50 days post AI. There was a significant difference between ram breeds in pregnancy rate (Finn 63.2 % v Romney 50.2 % ; P<0.05). There were no effects of inseminate dose nor of diluent. Time to onset of oestrus was affected by ewe live weight (P<0.05) with the heavier ewes showing a trend for an earlier onset but there was no overall effect of ewe weight on fertility. The effect of time to onset was reflected in an effect of time from CIDR removal to AI in the second half of the trial, with ewes AI’d within 30h of CIDR removal having a 10% lower fertility. These results indicate that acceptable fertility can be achieved with semen dose rates 5 to 10 fold less than normal, thereby increasing the number of inseminations available per ejaculate. Improved synchrony methods seem imperative to obtaining better fertility from AI.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 186-188, 1998
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