Características reprodutivas de éguas submetidas a um protocolo de indução de ovulação contendo progesterona e ECG

Abstract

Hormones aiming to induce and synchronize ovulations are usually used in mares intended for artificial insemination, donation or embryo reception. In this sense, progesterone (P4) by various routes of administration is useful for estrus synchronization. In cattle, the administration of equine chorionic gonadotropin (eCG) in intravaginal P4 protocols has been recommended for action on the development of anestrous cow follicles, improving ovulatory follicle area (FO), luteo body area (CL) and pregnancy rate. In mares, out-of-season ovulation can lead to early luteal regression (LRPR), reducing reproductive performance. RPCL may be related to ovulation of smaller follicles and/or deficiency in steroid secretion by FO. Although used in equine breeding in superovulation protocols, few studies have investigated the effect of ovulation inducers (GnRH or LH) corrected eCG on ovulatory characteristics, which could be of interest especially to mares outside that breeding season. Our hypothesis is that ovulatory synchronization with intravaginal P4 implantation associated with eCG may improve ovulatory follicle size (providing higher E2 production by it) and the quality of the subsequently formed CL (relating to higher P4 production by it). Thus, this study aims to monitor follicular development and evaluate ovulation time, FO and CL characteristics, as well as serum E2 and P4 levels, comparing the efficacy of two intravaginal P4-based ovulation synchronization protocols associated or not to eCG, in mares synchronized during the transitional season and during the breeding season. Fifteen mares between 03 and 08 years of age, crossbred, in good body condition were used. All animals were submitted to the same hormonal protocol based on 1.9g intravaginal P4 (1,9 g; CIDR®, Zoetis, São Paulo, Brasil) with an ovulation inducer (hCG; 1.750 UI (0,7 ml) Gonadotrofina Coriônica Humana; i.v.; Vetecor®, Hertape, Juatuba, Brasil) during the reproductive season (summer; period of regular cycling). Half of animals received intramuscular application of 400 UI (2ml; i.m.; Novormon®, Zoetis, São Paulo Brasil) de eCG (eCG group) while the other half received i.m. 2 ml of saline solution (control group). Data were compared by analysis of variance (tukey test) considering P<0.05. In the presente experimente ovulation was observed in 83% of the evalueted animals (ET: 67% of the animals e ER: 100% of the animals). For ovulation rate, a statistical difference was observed between the seasons (P=0.0042), but no difference was observed between the control ande eCG groups. (Controle: 79% dos animais e eCG 87,5%). There was still interection (P=0.0016) between season and treatment for ovulatory follicle diameter. In relation to the animals 9 that received eCG in the RE (33,00 ± 2,53 mm) they had smaller (P=0.0161) follicular diameter than those of ET (37.13 ± 1,76 mm) and smaller (P=0,0193) follicular diameter that the animals control the RE (36.56 ± 2,03 mm). Suggesting that the application of Ecg negatively affected the FO diameter in mares during RE. (26,60±4,44) Regarding the 13- day CL, its mean diameter was larger (P=0.0516) in mares that received eCG in RE(22,99±2,26). Addittionaly, there was a trend (P=0.0814) for a higher 13-day CL of animals receving eCG in ET (26,60±4,44) compared to animals not receiving eCG (control) from that same season(22,78±3,82).There was also a statistical tendency for later luteal regression (P=0.0625) in animals receiving eCG and in ET compared to animals receiving eCG in RE. In addition, a statistical tendency (P=0.0996) was observed for a higher amount of P4 at 13 days after ovulation in RE animals (5.84± 0.56 ng/ml) compared to ET animals (4.29± 0.63 ng/ml), suggesting greater luteal maintenance in animals during the summer. The application of eCG at the time of progesterone implant withdrawal delayed the time of luteal regression of the mares in the transition period, but its application was not beneficial to the mares of the reproductive season.