216 DINOPROST ADMINISTRATION, PERIOD OF OVULATION, AND OVULATORY FOLLICULAR SIZE ON DAYS FOUR TO SIX OF ESTROUS CYCLE IN EWES

The aim of this study was to evaluate the effects of 2 doses of dinoprost at the time of ovulation on Days 4 to 6 of the estrous cycle in ewes. The experiment was conducted in the city of Piau (Minas Gerais, Brazil) from July to August 2008 during the local no-breeding season. Twenty-four ewes with body condition score 3.0 ± 0.75 were used for this experiment. The estrous cycle was synchronized with intravaginal releasing devices containing 0.33 g of progesterone for 6 days (Eazi-Breed CIDR®, Pfizer Animal Health, Sao Paulo, Brazil), and 12.5 mg of dinoprost (Lutalyse®, Pfizer do Brasil Saude Animal, Sao Paulo, Brazil) laterovulvar plus 300 IU of eCG 24 h before device removal. Animals were monitored by transrectal ultrasonography every 8 h and subjected to 5 or 10 mg of dinoprost on Days 4, 5, or 6 of the cycle. Results were submitted to ANOVA and Tukey test, using all tests at the 95% confidence interval (SAEG program, Funarbe, Vicosa, Brazil). Data were reported as percentage or mean ± SD. The period from device removal to ovulation was 48.0 ± 7.07 h. The 5-mg dinoprost dose evoked similar (P > 0.05) results for Days 4, 5, and 6 regarding the time of ovulation after luteal gland regression induction [71.3 ± 28.6, 71.46 ± 30.4, and 68.2 ± 29.2 h for Days 4 (n = 4), 5 (n = 4), or 6 (n = 4), respectively] and follicle size (6.48 ± 0.34, 6.41 ± 0.35, and 6.5 ± 0.32 mm for Days 4, 5, and 6, respectively) at the time of ovulation. In animals that received 10 mg of dinoprost, the time of ovulation was affected (P ≤ 0.05) by Day of treatment [71.3 ± 27.6, 68.3 ± 30.6, and 64 ± 29.2 h for Days 4 (n = 4), 5 (n = 4), and 6 (n = 4), respectively]. However, there was no effect of the 10 mg on follicle size at ovulation (6.48 ± 0.34, 6.41 ± 0.35, and 6.3 ± 0.33 mm for Days 4, 5, and 6, respectively). There was no difference (P ≥ 0.05) on the size of ovulatory follicle(s) among animals with 1 (n = 4, 4, and 1 for Days 4, 5, and 6, respectively), 2 (n = 3, 3, and 4 for Days 4, 5, and 6, respectively), and 3 (n = 1, 1, and 3 for Days 4, 5, and 6, respectively) ovulations. The difference in the interval from luteal gland regression to ovulation in animals that received 10 mg of dinoprost on Day 6 of the estrous cycle suggests a higher sensitivity of corpora lutea at that moment. Results showed that both doses of dinoprost were capable of inducing early luteal gland regression; this fact supports the use of short-term protocols for the induction of estrus in ewes. Pfizer Brazil, CNPq, FAPEMIG.