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 Google Scholar Google Scholar Articles by Smith, M. F. Articles by Amoss, M. S. Search for Related Content PubMed PubMed Citation Articles by Smith, M. F. Articles by Amoss, M. S.

Pituitary and Ovarian Responses to Gonadotropin Releasing Hormone, Calf Removal and Progestogen in Anestrous Beef Cows^1,2,

Texas Agricultural Experiment Station, Beeville 78102 and and West Virginia Agricultural and Forestry Experiment Station, Morgantown 26506

Abstract

Effects of Syncro-Mate B (SMB) and(or) short-term calf removal (CR) on pituitary and ovarian responses after gonadotropin releasing hormone (GnRH) were studied in two experiments. In Exp. 1, 24 thin, 2-yr-old, anestrous, Brahman crossbred cows were allotted randomly to a 2 x 2 factorial design involving 27-h CR and SMB. All cows were injected (iv) with 150 µg GnRH at 24 h after removal of implants and(or) calves. Blood samples were collected at –30, 0, 15, 30, 45, 60, 90, 120 and 180 min post-GnRH. The GnRH-induced release of luteinizing hormone (LH) differed among treatments (P<.05). The release of LH was higher in cows with CR than in control cows (P<.05). Although pretreatment with SMB increased the quantity of LH release compared with the CR and control cows, SMB + CR did not show an additive effect over SMB alone. In Exp. 2, 49 mature Charolais x Hereford cows were allotted randomly to one of the following groups: control, 24-h CR or 32-h CR. Follicular size was measured by palpation per rectum at the time of CR. All cows received 300 jug GnRH (im) at 24 h after CR, at which time calves were returned to cows in the 24-h CR group. The pattern of release of LH over time was similar to the control and 24-h CR groups; however, LH release was greater (P<.05) in the 32-h CR group. A linear effect of follicular size on the pattern of release of LH after GnRH injection was observed regardless of treatment. Plasma concentration of progesterone at 7 and 14 d after GnRH, indicated that function and lifespan of the induced corpora lutea were not altered by CR or follicular size. These results indicate that pretreatment with SMB increased the release of LH to exogenous GnRH. Furthermore, CR also increased the responsiveness of the pituitary to GnRH, provided that the calves were not returned during the period of induced LH release.

¹ Published with the approval of the Director of the Texas A&M Univ. System as Scientific Series Paper No. TA17688 and the approval of the Director of the West Virginia Agr. and Forestry Exp. Sta. as Scientific Paper No. 1749.

² The authors express their appreciation to M. Wright, W. C. Burrell, B. N. Songster, L. P. Stevens, W. L. Ferrell and W. V. Thayne for their technical assistance.

³ Present address: Dept. of Anim. Sci., Univ. of Missouri, 160 Animal Science Research Center, Columbia 65211.

⁴ Statistician for the Missouri Agr. Exp. Sta.