Abstract
Fifty Border Leicester × Scottish Blackface ewes superovulated with 16 mg of porcine follicle stimulating hormone (p-FSH) were used to test the effects on ovulation and ovum quality of five oestrous synchronisation treatments (n=10 per treatment) applied during the breeding season. The treatments were a controlled internal drug release (CIDR) device containing 330 mg progesterone (T1), a 30 mg fluorogestone acetate (FGA) pessary (T2), a 30 mg FGA pessary in which the FGA was redistributed on the sponge matrix (T3), a 30 mg FGA pessary plus 400 mg of progesterone (T4) and an injection of 125 μg of the prostaglandin (PGF2α) analogue, Cloprostenol, on Day 12 following oestrus (T5). Ewes were inseminated (Day 0) by the laparoscopic intrauterine method at 60 h after either ‘progesterone/progestagen’ withdrawal (T1–T4) or PGF2α injection (T5). Mean (±SEM) ovulation rates were 3.5±1.0 (T1), 7.9±1.1 (T2), 6.9±1.3 (T3), 8.8±1.4 (T4) and 5.4±1.7 (T5) (P<0.05 for T1 vs. T2 and T1 vs. T4). Corresponding values for the proportion of ova recovered by laparoscope on Day 6 were 0.46, 0.40, 0.42, 0.68 and 0.44. The greatest number (4.1±0.9) of high quality ova (compact morulae and blastocysts) was obtained with T4. The results indicate that for ewes superovulated with p-FSH, a higher level of steroid priming than that supplied by either a CIDR device or a 30 mg FGA pessary is desirable.
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