Gnrh

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 J Anim Sci 1993. 71:185-198.

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Administration of GnRH at Estrus Influences Pregnancy Rates, Serum Concentrations of LH, FSH, Estradiol-17@, Pregnancy-Specific Protein B, and Progesterone, Proportion of Luteal Cell Types, and In Vitro Production of Progesterone in DairyCows'
Michael 0. Mee*92, Jeffrey S. Stevenson*-3, Brenda M. Alexander?, and R. Garth Sassed
*Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201 and ?Department of Animal Science, University of Idaho, Moscow 83843

Four experiments were conducted to examine effects of GnRH administered at estrus on various reproductive characteristics in repeat-breeding dairycows (eligible for third service). In Exp. 1, cows ( n = 8 per group) received (i.m.) either saline or 50, 100, or 250 pg 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= .lo) through 16 d after estrus in nonpregnant cowsthat 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= .lo) in those given GnRH than in those given saline. In Exp. 2, concentrations of LH, FSH, and estradiol-17P (Ez) weresimilar among 12 cows during the periestrual period before they received (i.m.1 100 pg 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, agreater 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-

ABSTRACT

treated cows on d 1, 3, and 8, but overall concentrations of LH were reduced ( P< .05) in GnRH-treated cows. Concentrations and number ofpulses 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 f 12 h ) , with higher ( P< .05) concentrations of P4 on d 4 to 8. In Exp. 4, eight cows received either 100 pg of GnRH or saline at 12 h after onset of estrus (d 0 ) in a cross-over design. Invitro basal production of P4 (micrograms per gram) by luteal slices from d-10 corpora lutea ( C L ) was similar between treatments before and after 2 h of incubation, but luteal slices from cows previously treated with GnRH produced less ( P< .05) P4 in the presence of LH than did tissue from saline-treated cows. Corpora lutea had a greater ( Pc .05) proportion of large luteal cells (31 vs 14%) and alesser ( P< .05) proportion of small luteal cells (69 vs 86%) in GnRHthan in saline-treated cows. We concluded that administration of GnRH at estrus in repeat-breeding dairy cows increased concentrations of P4 in serum earlier after ovulation and maintained higher concentrations of P4 for up to 40 d after treatment (during pregnancy), which seemed to be associated with higher embryonic survival...