HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Troxel, T. R. Articles by Carlin, S. E. Search for Related Content PubMed PubMed Citation Articles by Troxel, T. R. Articles by Carlin, S. E.

Ovulation and Reproductive Hormones following Steroid Pretreatment, Calf Removal and GnRH in Postpartum Suckled Beef Cows

University of Illinois, Urbana 61801

Abstract

Two experiments were conducted to determine the effect of calf removal, steroid pretreatment and treatment with gonadotropin releasing hormone (GnRH) on subsequent reproductive hormone secretion and ovulation. In the first experiment, GnRH was administered to postpartum beef cows at two levels (100 and 250 µg) and in two carrier vehicles (saline and carboxy-methylcellulose [CMC]). Although peak luteinizing hormone (LH) concentrations were similar for all cows, the interval from treatment to peak LH release and the duration of the LH release was prolonged (P<.05) in the cows that were given GnRH in CMC. In the second experiment, 30 postpartum suckled beef cows were assigned to a 2 x 3 factorial experiment, with calf removal (none or short-term) and steroid pretreatment (none, norgestomet implant or Synchro-Mate B) as main effects. Short-term calf removal consisted of a 36-hr nonsuckling period beginning at the time of implant removal. GnRH (250 /µg in CMC) was injected subcutaneously 24 hr after implant and calf removal. An increased GnRH-induced LH release due to short-term calf removal (P<.05) and steroid pretreatment (P<.10) was detected. The interaction was not significant, however, (P<.25). Therefore, the suckling-induced suppression of pituitary LH release to exogenous GnRH can be at least partially eliminated within 24 hr of calf separation or norgestomet implant removal. The GnRH-induced LH release was correlated with pretreatment concentrations of estradiol-17β for cows that were not separated from their calves (r = .61; P<.05) but not for cows that were subjected to short-term calf removal (r = .28; P>.10). Ovulation occurred in all cows (100%) that were separated from their calves and given GnRH, whereas only 67% of cows not subjected to calf removal ovulated following GnRH treatment. Although the ovulation responses differed (P<.025) between cows that were and were not separated from their calves, ovulation response was not affected by steroid pretreatment (P>.10).

¹ GnRH and norgestomet implants and Synchro-Mate B were generously supplied by Drs. R. H. Rippel (Abbott Laboratories) and S. E. Mares (Searle Agriculture, Inc. ). Drs. G. N. Niswender and N. R. Mason generously supplied antisera for radioimmunoassay of LH (B-225) and estrone and estradiol-17β. Purified bovine LH (LER-1072-2) was supplied by Dr. L. E. Reichert and the NIH-LH-B10 was supplied by the National Institute of Arthritis, Metabolism and Digestive Diseases.

² This research was conducted as part of regional research project NC-113, Methods for Improvement of Fertility in Cows Postpartum.

This article has been cited by other articles:

				T. M. Prado, R. P. Wettemann, L. J. Spicer, J. A. Vizcarra, and G. L. Morgan Influence of exogenous gonadotropin-releasing hormone on ovarian function in beef cows after short- and long-term nutritionally induced anovulation J Anim Sci, December 1, 2002; 80(12): 3268 - 3276. [Abstract] [Full Text] [PDF]