Does hCG administration increase the incidence of double and multiple ovulations in Campolina mares with co-dominant follicles?

Abstract

The human chorionic gonadotrophin (hCG) has been routinely used in the equine species to induce ovulations for more thanfour decades. The incidence of multiple ovulations in horses is variable, being double ovulations a common occurrence insome Brazilian breeds, such as Brasileiro de Hipismo and Campolina. The aim of this work was to evaluate the role of hCGadministration to increase, in Campolina mares, the incidence of double and multiple ovulations, which are desirable inembryo transfer programs. One hundred and four (104) mares had their estrous cycles recorded through rectal palpation andultrasonographic evaluation during the breeding season of 2003 - 2004, in a total of two hundred and eight (208) cycles (twocycles per mare). Animals were allocated in two groups, with fifty two (52) horses each. In Group I mares, once one or more= 35 mm follicles and grade 2 uterine edema were present, 2.500 IU of hCG were intravenously administered. The untreatedmares in Group II served as control. The Chi-Square test was used to analyze obtained results. The incidence of doubleovulations in groups I and II was, respectively, of 32.7% (34/104) versus 30.8% (32/104). The incidence of triple ovulations waslow in both groups, of 1.9% (2/104). Only once in the control group (1.0% - 1/104) was a quadruple ovulation detected. Therewas no difference in the incidence of double and multiple ovulations between both groups (p > 0.05). Possibly, hCG administrationdid not influence ovulation patterns in this work due to the fact that Campolina breed mares physiologically show a considerableincidence of double and multiple ovulations.