Ovarian response in the estrual cat receiving varying dosages of HCG

Laparoscopy was utilized to determine the ovulatory response of the domestic cat to various dosages of human chorionic gonadotropin (HCG) administered intramuscularly at one or two time periods during estrus. A linear HCG dose-ovulatory response was observed in queens receiving 0--500 IU HCG as a single injection on day 1 or as injections given on days 1 and 2 of estrus. Animals treated with 500 IU HCG on day 1 or days 1 and 2 of estrus produced the maximum percent ovulation rates based on pre- and post-HCG ovarian morphology observation by laparoscopy (100.0, 95.9%, respectively). A single injection of 500 IU HCG produced a significant increase (p less than 0.05) in mean percent ovulation rate in comparison to the 0, 50 and 100 IU HCG single injections. Administration of 500 and 250 IU HCG for 2 days of estrus resulted in a greater percent ovulation rate than the 2-day injection of 50 IU (p less than 0.05). These results indicate that the proportion of mature follicles ovulating in an induced ovulator, such as the cat, is an increasing function of graded dosages of exogenous hormone.