The use of biotechnology, such as AI, embryo transfer, and hormonal protocols, have accelerated the genetic improvement in the equine specie, and inducers of ovulation, such as hCG, are important tools in implementing them. However, the repeated use of ovulation inducers can promote the development of antibodies and undermine their purpose. Thus, a synthetic GnRH, deslorelin, has been used. In this study, we compared the reproductive performance of 44 Mangalarga Marchador donor mares, aged between 5 and 21 years and with sound reproductive history after treatment with hCG or deslorelin. During estrus, mares were examined by transrectal ultrasonography every other day until a follicle of 30 mm in diameter was detected and then daily until detection of a >35-mm follicle and moderate uterine edema. At this time, mares were treated with either 2 mL of saline, i.m. as controls (CON = 16); 2500IU of hCG, i.v. (Chorulon, Intervet Inc., Millsboro, DE, USA; hCG = 14); or 2 mg mL-1 deslorelin in BRT vehicle (BET Pharm, Lexington, KY, USA), i.m. (DES = 14). After treatments, mares were examined at 12-h intervals until ovulation and were inseminated with fresh semen 12 h after ovulation. On Day 8, embryos were recovered and evaluated. All mares were ovulated, and follicle diameters were not different (P > 0.05) at the time of treatment (38 ± 0.029 v. 39 ± 0.029 v. 38 ± 0.029 mm). Embryo recovery was similar among groups (CON, 37.5%; hCG, 42.8%; DES, 50.0%, respectively). The interval from treatment to ovulation did not differ (P > 0.05) between hCG (1.43 +0.56 days) and DES mares (1.14 + 0.36 days), and both were less (P > 0.05) than for controls (CON, 2.94 + 0.77 days). The number of mares that ovulated per ovulation interval were as follows: <24 h = CON: 0%, hCG: 7.14%, and DES: 14.29%, respectively; from 24 to 48 h = 6.25%, 64.29%, and 78.57%; from 49 to 72 h = 37.5%, 28.57%, and 7.14%; >72 h = 56.25%, 0%, and 0%. Time to ovulation was negatively correlated (P < 0.05) with follicle diameter in CON (r = -0.50, P < 0.05) but not for hCG (r = 0.05) or DES (r = 0.022) and was positively correlated with embryo recovery for DES (r = 0.46, P < 0.10), but not hCG (r = 0.23) or CON (r = 0.09). Based on the results, we concluded that hCG and DES effectively synchronize the time of ovulation. Follicle size did not affect the time of ovulation in hCG- and DES-treated mares.
We thank the Farm Water supply for the animals and drugs.
Embryo Transfer