Dynamics of gonadotropin release following ovariectomy and injection of gonadotropin-releasing hormone in early postpartum dairy cows.
The influence of the ovary and of injection of low doses of gonadotropin-releasing hormone on secretion and gonadotropin-releasing hormone-induced release of gonadotropins in early postpartum cows was examined in a 2 x 2 factorial design (6 cows/group). Twelve cows were ovariectomized 2 d postpartum (calving = d 0; groups 1 and 2) and 12 cows were left intact (groups 3 and 4). Groups 1 and 3 received gonadotropin-releasing hormone (5 micrograms) every 120 min for 70 h from d 6 to d 9; groups 2 and 4 received saline by the same regimen. All animals received 50 micrograms gonadotropin-releasing hormone on d 9. Mean concentrations of FSH were higher following ovariectomy compared with those of intact cows 6 to 8 d postpartum, whereas no differences in FSH were observed between cows receiving gonadotropin-releasing hormone or saline during this period. Concentrations of LH were similar in intact and ovariectomized cows on d 6 to 8 but were increased in cows receiving gonadotropin-releasing hormone compared with cows receiving saline. Ovariectomy did not alter the gonadotropin-releasing hormone-induced release of gonadotropins on d 9. Injection of gonadotropin-releasing hormone on d 6 to 8 resulted in a decreased gonadotropin-releasing hormone-induced release of gonadotropins on d 9. It was concluded that removal of ovarian influence resulted in increased secretion of FSH but did not affect gonadotropin-releasing hormone-induced release of LH and FSH during the early postpartum period.
Dissen
G A
GA
Department of Dairy Science, University of Missouri, Columbia 65211.
Mollett
T A
TA
Youngquist
R S
RS
Garverick
H A
HA
D000818:Animals; D002417:Cattle / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy / Q000662:veterinary; D010053:Ovary / Q000502:physiology*; D010906:Pituitary Hormone-Releasing Hormones / Q000008:administration & dosage / Q000494:pharmacology*; D049590:Postpartum Period / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy
D010906:Pituitary Hormone-Releasing Hormones; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone