Induction of ovulation with gonadotropin-releasing hormone during proestrus in cattle: influence on subsequent follicular growth and luteal function.

摘要

The effects of exogenous GnRH, given before the expected physiological LH surge, on oestradiol secretion of the ovulatory follicle, occurrence of ovulation, development and function of the corpus luteum, and growth of a dominant follicle after ovulation in cattle were examined. Luteolysis was induced by cloprostenol in 3 cows and 6 heifers. Animals received either a single dose (0.1 mg) of GnRH (gonadorelin) 24, 48, or 72 h after cloprostenol treatment, or no GnRH (controls). Ovaries were scanned by ultrasound and blood samples were collected for measurement of progesterone and oestradiol-17beta concentrations. Growth curves of dominant follicles differed significantly (P<0.01) between cattle treated with GnRH 24 h after cloprostenol treatment andcontrol animals. One day after ovulation, the diameter of the dominant follicle was almost 1 mm larger in animals that had received GnRH 24 h after cloprostenol treatment compared with controls. This difference remained almost unchanged during the entire follow-up period. The recruitment of a new follicular wave after ovulation occurred earlier in animals that received GnRH 24 h after cloprostenol treatment than in animals from other the other treatment groups. Development of corpora lutea and levels and profiles of progesterone production were unaffected. When GnRH was given 1 day after cloprostenol injection, 2 animals showed significantly different development of corpora lutea (P<0.05) and progesterone production (in terms of concentrations (P<0.05) and profiles (P<0.01)). After normal ovulation and corpus luteum development, luteolysis took place on days 5 or 6 after ovulation, and animals ovulated on days 9 and 10. It is suggested that early induction of ovulation with GnRH can cause shortened luteal function in cattle and, ultimately, reduced fertility.