Abstract

Twelve, 10-month old ewe hoggets (Av LW 32.5 kg) were placed in metabolism crates under controlled lighting (11 h L:13 h D) for a 9 d adaptation period and were fed for maintenance. They were synchronized by vaginal insertion of CIDR and treated with gonadotrophins for superovulation. Of the 12 hoggets 9 had two or more successive plasma samples with > 0.9 ng/ml progesterone (P4) indicating they had ovarian activity prior to treatment. Mean P4 concentrations prior to treatment (d - 3) were 0.69 ± 0.18 ng/ml and had risen to 1.50 (± 0.38), 1.72 (±0.35), 1.36 (±0.11) and 1.31 (±0.10) ng/ml for d 0 to d 3 of treatment. On d 9, 10 and 11, prior to CIDR removal, P4 levels were back to base line levels (0.60, 0.46 and 0.57 (±0.06) ng/ml respectively). The mean number of follicles and corpora lutea were 5.0 (±0.95) and 1.8 (±0.53), respectively. Total CL had a negative correlation (r = -0.64, P<0.05) with the P4 concentration on the day of CIDR removal. Six of the 12 ewes had an LH peak within 25 hours after CIDR removal. In addition, those ewes treated during late cycle tended (P>0.10) to have a better ovarian response than those treated at early or mid cycle. These results suggest it may be necessary to use two CIDR to maintain a sufficiently long period of P4 elevation. In addition, the day of the cycle that the CIDR is inserted may be important to achieve maximum response from ovulation enhancement treatment in ewe hoggets.

JW, Campbell, MF McDonald, and GA Wickham

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 239-242, 1994