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 Parfet, J. R. Articles by Moss, G. E. Search for Related Content PubMed PubMed Citation Articles by Parfet, J. R. Articles by Moss, G. E.

Anterior Pituitary Concentrations of Gonadotropins, GnRH-Receptors and Ovarian Characteristics Following Early Weaning in Beef Cows^1,2,3,4,

Purdue University^,7, West Lafayette, IN 47907

Abstract

Endocrine changes in the hypophyseal-ovarian axis associated with early calf removal were investigated in anestrous beef cows. Tissues were collected and analyzed from multiparous beef cows slaughtered at 0 (n=8), 36 (n=8) or 72 h (n=8) after calf removal during the fifth week after calving. Cows that 1) exhibited estrus; 2) had postmortem signs of a recent ovulation or 3) had serum concentrations of luteinizing hormone (LH) indicative of an ovulatory surge, were excluded from the analysis. Five control cows that were not slaughtered exhibited estrus from 30 to 84 h after calf removal. Seven additional cows were continuously kept with their calves and did not exhibit estrus until 72 ± 9 d after calving. Serum concentrations of estradiol-17ß (estradiol) averaged 8.2 ± 1.7, 7.5 ± 2.0 and 9.1 ± 1.5 pg/ml at 0, 36 and 72 h, respectively, but they averaged 22.8 ± 4.7 pg/ml prior to estrus in control cows. Therefore, observations were assumed to represent events that occur prior to the rise in serum concentrations of estradiol that occurs during proestrus. Volume of fluid from the largest ovarian follicle tended to be greater (P<.10) at 72 h (1.5 ± .2 ml) than at 0 h (1.1 ± .1 ml) or 36 h (1.0 ± .1 ml). Follicular-fluid concentrations of estradiol, but not progesterone, were positively correlated (P<.01) with follicular volume. However, numbers of small (<100 µl), medium (100 to 400 µl) and large follicles (>400 µl) as based on fluid volume, as well as follicular-fluid concentrations of estradiol and progesterone, did not differ among treatment groups. Calf removal did not affect the following anterior pituitary characteristics: concentrations of follicle-stimulating hormone (FSH) or LH, number of receptors for gonadotropin-releasing hormone (GnRH) or in vitro responsiveness of dispersed anterior pituitary cells to GnRH. In summary, the absence of estrous cycles in suckled beef cows, near 30 d postpartum, is apparently not due to deficiencies in 1) ovarian follicular development, 2) anterior pituitary concentrations of LH and FSH or in vitro releasibility of LH or 3) pituitary receptors for GnRH.

¹ Journal paper no. 10275, Purdue Univ., Agr. Exp. Sta.

² Presented in part at the 76th Annu. Meet. of the Amer. Soc. of Anim. Sci., Columbia, MO, Abstr. #442.

³ The authors express appreciation to Doris Blair, Sharon Frank and Amy Hines for their invaluable technical expertise; J. Rivier, The Salk Inst., San Diego, CA, for the gift of GnRH analog; G. D. Niswender, Colorado State Univ., for supplying antiserum to progesterone and LH; D. J. Bolt, USDA, Beltsville, MD, for supplying reagents for the FSH radioimmunoassay; N. R. Mason, Eli Lilly and Co., Indianapolis, IN, for providing antiserum to estradiol-17ß; and the Natl. Pituitary Agency for providing iodination grade LH.

⁴ Supported in part by USDA grant no. 59-2181-1-2-026-0.

⁵ Present address: Dept. of Dairy Sci., Univ. of Missouri, Columbia, MO 65211.

⁶ Reprint requests. Present address: Dept of Anim. Sci., Univ. of Wyoming, Laramie, WY 82071.

⁷ Dept. of Anim. Sci.