Comparação de dinoproste trometamina e acetato de deslorelina como indutores ovulatórios em éguas

Abstract

Among the inducing hormones of equine ovulation, deslorelin acetate (DA;Sincrorrelin ® , Ouro Fino, Brasil), a synthetic analogue of gonadotrophin releasing hormone (GnRH), is well known, with proven efficacy in equine reproductive season programs. Prostaglandins play several roles in the animal body, with prostaglandin F2-alfa (PGF2α) being a potent luteolytic agent, and its biologic functions in the ovulation mechanism have been studied. Dinoprost tromethamine (DT;Lutalyse ®, Pfizer, EUA), analogous to PGF2α, may have benefits when used in combination with other hormones in equine reproductive season programs. This dissertation presents a chapter. The objective was to determine the efficiency of DT and its association with the synthetic analogue of GnRH, DA in inducing ovulation of cyclic mares and in improving gestational rate. Mangalarga mares (n=30), aged between 4 - 15 years and body condition score 5 - 6 were examined daily via transrectal ultrasonography. Edema 2, open cervix and a follicular diameter of at least 35 mm were minimum conditions of mares inclusion in this study. Estrous cycles (n=52) were allocated to one of five treatments: treatment 1 (n= 17) 7.5 mg of DT treatment 2 (n= 10), 1.0 mg of DA (positive control); treatment 3 (n= 4), 0.5 mg of DA (negative control); treatment 4 (n= 7), 1.0 mg of DA + 7.5 mg of DT and treatment 5 (n = 14), 0.5 mg of DA + 7.5 mg DT. The animals were examined every 6 hours – Dominant follicle diameter and endometrial edema were recorded until ovulation and pregnancy diagnosis performed at 12 days post ovulation. Number of treatments performed (52) and number of gestational diagnoses were recorded (52). Data were analyzed by SAS ® , (Cary - NC, USA) procedures. Gestation data were submitted to chi-square analysis using the GENMOD procedure with the binomial option. Ovulation rates (%) were 62.5, 90, 75, 100 and 92.31 for treatments 1-5, respectively and differ among treatments1 to others. Effects of treatment, transitional period, pre-ovulation edema and dominant follicle class were considered significant if p<0.05. The mean time-interval between induction and ovulation was 54.52 ± 5.19 h (17-184 h). Mean pre-ovulatory follicle diameter (39.71±0.23 mm and median 39.7mm) did not differ among treatments. There was no effect of treatment (p= 0.67) and transitional period (p= 0.81) on gestation rate. Gestation rates were not affected by edema at the time of induction (p= 0.66), pre-ovulatory follicle diameter class (p= 0.96) and pre-ovulatory edema (p= 0.45). The similar ovulation rates obtained in this trial, support the hypothesis that the associations between prostaglandin and GnRH analogues may sustain the ovulatory mechanism compared to the individual use of the latter. This complimentary effect may reduce the cost of synchronization protocols currently used which rely solely in the more expensive GnRH analogues. The results corroborate the active role of prostaglandins in the ovuluation mechanism.