Low sperm numbers and ambient temperature storage are two important factors in the successful AI system for dairy cattle in New Zealand. A critical evaluation of these factors with ram semen is required before the establishment of a similar AI system within the NZ sheep industry is feasible. A trial involving a total of 1262 Romney ewes was conducted in April 1998 to examine the effects of inseminate dose (25, 5, 1 and 0.5 x 106 sperm) of semen held for up to 9 h at 20°C in two diluents (RSD-1 and RSD-8). Ewes, synchronised with 3 types of CIDR devices were laparoscopically AI`ed with semen from either a Finn or a Romney ram at set times (49 or 56h) after CIDR removal. AI was spread over 4 days in each of two consecutive weeks. Rams were used on each alternative day. Ewes were checked for return to service to determine pregnancy. There was a significant (P<0.001) difference between rams in pregnancy rate (Finn =35.6 and Romney =52.5%). There was an effect (P<0.001) of inseminate dose (25 = 55.5 ± 2.6%; 5 = 45.2 ± 2.6%; 1 = 37.2 ± 2.6% and 0.5 = 37.5 ± 2.6%). However there was a suggestion of an overall dose by ram interaction with the Romney semen maintaining higher fertility at lower dose levels. There were no effects of inseminator or of diluent. Time from CIDR removal to oestrus had a significant (P<0.05) effect. Time to onset of oestrus was affected by CIDR type. While there was no overall effect of CIDR type on fertility, there was a significant (P<0.05) interaction between sperm dose and CIDR type. These results indicate that acceptable (>50%) fertility can be achieved with sperm dose rates as low as 1.0x106 if semen quality is satisfactory thus increasing the number of inseminates per ejaculate 20-50 fold. Improved synchrony methods seem imperative to obtaining better fertility from AI.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 219-222, 1999
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