Journal of Animal Science, Vol 71, Issue 1 185-198, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Administration of GnRH at estrus influences pregnancy rates, serum concentrations of LH, FSH, estradiol-17 beta, pregnancy-specific protein B, and progesterone, proportion of luteal cell types, and in vitro production of progesterone in dairy cows

M. O. Mee, J. S. Stevenson, B. M. Alexander and R. G. Sasser
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201.

Four experiments were conducted to examine effects of GnRH administered at estrus on various reproductive characteristics in repeat-breeding dairy cows (eligible for third service). In Exp. 1, cows (n = 8 per group) received (i.m.) either saline or 50, 100, or 250 micrograms of GnRH at 12 h after onset of estrus. There was a positive linear (P < .05) effect of dose on concentrations of LH, but not of FSH, in serum at 2 h after the injection. Concentrations of progesterone (P4) were higher (P = .10) through 16 d after estrus in nonpregnant cows that returned to estrus 18 to 24 d after GnRH treatment than in nonpregnant cows given saline. Likewise, among cows with elevated concentrations of P4 through 30 d after estrus (diagnosed pregnant by increased concentrations of pregnancy-specific protein B; PSPB), P4 was higher (P = .10) in those given GnRH than in those given saline. In Exp. 2, concentrations of LH, FSH, and estradiol-17 beta (E2) were similar among 12 cows during the periestrual period before they received (i.m.) 100 micrograms of GnRH or saline at estrus. Concentrations of P4 after estrus were increased 2 d earlier (P < .05) in GnRH- than in saline-treated cows. Among cows with elevated concentrations of P4 and PSPB through 40 d after AI, P4 was higher (P < .05) in those given GnRH than in those given saline. In Exp. 1 and 2, a greater proportion (43 vs 14%; P = .07) of cows given GnRH was pregnant 42 to 56 d after estrus than of those given saline, but calving rate was similar (27 vs 14%). In Exp. 3, average number of LH pulses per 8 h was similar between saline- and GnRH-treated cows on d 1, 3, and 8, but overall concentrations of LH were reduced (P < .05) in GnRH-treated cows. Concentrations and number of pulses of FSH were increased (P < .05) on d 8 after treatment with GnRH. Concentrations of P4 were increased earlier (P < .05) after estrus in GnRH-treated (69 +/- 12 h) than in saline-treated cows (126 +/- 12 h), with higher (P < .05) concentrations of P4 on d 4 to 8. In Exp. 4, eight cows received either 100 micrograms of GnRH or saline at 12 h after onset of estrus (d 0) in a cross-over design.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				J. S. Stevenson, M. A. Portaluppi, D. E. Tenhouse, A. Lloyd, D. R. Eborn, S. Kacuba, and J. M. DeJarnette Interventions After Artificial Insemination: Conception Rates, Pregnancy Survival, and Ovarian Responses to Gonadotropin-Releasing Hormone, Human Chorionic Gonadotropin, and Progesterone J Dairy Sci, January 1, 2007; 90(1): 331 - 340. [Abstract] [Full Text] [PDF]

				C. B. Sellars, J. C. Dalton, R. Manzo, J. Day, and A. Ahmadzadeh Time and Incidence of Ovulation and Conception Rates After Incorporating Estradiol Cypionate into a Timed Artificial Insemination Protocol J Dairy Sci, February 1, 2006; 89(2): 620 - 626. [Abstract] [Full Text] [PDF]

				M. A. Portaluppi and J. S. Stevenson Pregnancy Rates in Lactating Dairy Cows After Presynchronization of Estrous Cycles and Variations of the Ovsynch Protocol J Dairy Sci, March 1, 2005; 88(3): 914 - 921. [Abstract] [Full Text] [PDF]

				T.L. Davis, M.L. Mussard, H. Jimenez-Severiano, W.J. Enright, and J.E. Kinder Chronic Treatment with an Agonist of Gonadotropin-Releasing Hormone Enhances Luteal Function in Cattle Biol Reprod, August 1, 2003; 69(2): 398 - 403. [Abstract] [Full Text] [PDF]

				M. Kaim, A. Bloch, D. Wolfenson, R. Braw-Tal, M. Rosenberg, H. Voet, and Y. Folman Effects of GnRH Administered to Cows at the Onset of Estrus on Timing of Ovulation, Endocrine Responses, and Conception J Dairy Sci, June 1, 2003; 86(6): 2012 - 2021. [Abstract] [Full Text] [PDF]