Effect of repeated low doses of gonadotropin-releasing hormone on the secretion of luteinizing hormone and follicle-stimulating hormone, and ovarian function in dairy cows suffering from anovulation type I.

ABSTRACT

The aim of the study was to evaluate the effect of repeated low doses of gonadotropin-releasing hormone (GnRH) agonist buserelin once a day for 5 days on follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release, and ovarian function in dairy cows with anovulation type I. The study was conducted on 10 anovulatory Polish Holstein-Friesian cows. Cows in Group 1 (n = 5) received 4 µg of buserelin intramuscularly. once a day for 5 days. Control cows from Group 2 (n = 5) received saline. Concentrations of progesterone, FSH, and LH in the blood were analysed using radioimmunoassay (RIA). Ovarian structures were monitored weekly after the end of treatment by ultrasound for 4 weeks. Injections of buserelin increased FSH and LH concentrations. Release of FSH and LH was largely variable, but there was significant (P < 0.001) interaction between time and treatment during all treatment days. The number of follicles in the treatment group was significantly greater (P = 0.029) than in the control group on day 5, the diameter of follicles on day 12 was also larger (P < 0.01) in treated than in control cows. Ovulation occurred in 4 of the 5 treated cows, but only in 1 of the control cows in the 40 days after treatment. In conclusion, repeated low doses of GnRH analogue buserelin once a day for 5 days may increase the concentration of FSH and LH in dairy cows with anovulation type I.