Endocrine responses and ovarian changes in inseminated dairy heifers after an injection of a GnRH agonist 11 to 13 days after estrus

• Published in: Journal of animal science Vol. 70; no. 2; p. 508
• Main Authors: Rettmer, I, Stevenson, J S, Corah, L R
• Format: Journal Article
• Language: English
• Published: United States 01.02.1992
• Subjects: Animals; Cattle - physiology; Corpus Luteum - diagnostic imaging; Corpus Luteum - drug effects; Corpus Luteum - physiology; Estradiol - blood; Female; Fertilization - drug effects; Follicle Stimulating Hormone - blood; Gonadotropin-Releasing Hormone - administration & dosage; Gonadotropin-Releasing Hormone - analogs & derivatives; Gonadotropin-Releasing Hormone - pharmacology; Hormones - administration & dosage; Hormones - blood; Hormones - pharmacology; Injections - veterinary; Insemination, Artificial - veterinary; Luteinizing Hormone - blood; Ovarian Follicle - diagnostic imaging; Ovarian Follicle - drug effects; Ovary - diagnostic imaging; Ovary - drug effects; Pregnancy; Progesterone - blood; Random Allocation; Ultrasonography
• ISSN: 0021-8812
• DOI: 10.2527/1992.702508x

Our objective in this study was to determine endocrine responses and changes in ovarian structures after a single injection of a GnRH agonist in Holstein dairy heifers (n = 38). Heifers were inseminated and received (i.m.) either saline or 200 micrograms of fertirelin acetate once on d 11, 12, or 13 after estrus (d 0). Blood was collected at 15- to 30-min intervals for 6 h after the injection to determine concentrations of LH, FSH, estradiol (E), and progesterone (P) in serum and once daily for 8 to 12 d after the injection to determine concentrations of E and P. Pregnancy rates were 58% (11 of 19) in both treatment groups. Diameter of the corpus luteum and numbers and appearance of ovarian follicles were determined by real-time ultrasonography on d-1 through 5 after injection. No treatment-induced ovulations or changes in the number of ovarian follicles were observed after the injection of the GnRH agonist. More (P less than .05) of the largest follicles within heifers receiving fertirelin acetate showed changes in their appearance on at least the 1st d after injection (6 of 10 vs 1 of 9 control heifers). Fertirelin acetate induced release of LH and FSH from the pituitary within 15 min of injection; both hormones reached peak concentrations at 120 min and then returned to pretreatment concentrations by 300 to 360 min after injection.