These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


PUBMED FOR HANDHELDS

Search MEDLINE/PubMed


  • Title: Effect of suckling on pituitary responsiveness to gonadotropin-releasing hormone throughout the early postpartum period of beef cows.
    Author: Williams GL, Kotwica J, Slanger WD, Olson DK, Tilton JE, Johnson LJ.
    Journal: J Anim Sci; 1982 Mar; 54(3):594-602. PubMed ID: 6806232.
    Abstract:
    The objective of this study was to compare pituitary responsiveness to gonadotropin-releasing hormone (GnRH) throughout the early postpartum period (PP) in beef cows suckling in single calf vs cows which had calves removed at birth. The experiment utilized 48 cows in a 2 X 4 factorial. Main effects studied were suckling status (suckled or nonsuckled) and days PP (d 3, 10, 20 or 30). Covariates studied were pre-treatment concentrations of progesterone (P), estradiol-17 beta (E), luteinizing hormone (LH) and follicle stimulating hormone (FSH). Suckled (S) cows nursed one calf, while nonsuckled (NS) cows had calves removed at birth. Treatment was a single im injection of 100 micrograms GnRH dissolved in saline. Pre-GnRH plasma concentrations of E, P, LH and FSH and post-treatment plasma concentrations of LH and FSH were determined at 15 min intervals (-30 to 360 min) in blood samples collected via jugular cannulae. Post-treatment plasma concentrations of P were determined at 6 (n = 23) or 8 (n = 23) days after treatment to monitor ovarian response. Concentrations of E, LH and FSH before GnRH injection did not differ (P greater than .1) between S and NS cows at any PP stage and data were pooled for statistical analyses. Pre-treatment LH, but not FSH, increased (r = .43; P less than .002 (with days PP and concentrations of LH were greater (P less than .05) at 30 d than at 3 d PP. Pre-treatment P was greater (P less than .05) in NS than in S cows on d 30 PP and P was correlated (r = .51; P less than .01) with days PP in NS cows. However, the frequency of cows exhibiting plasma P greater than or equal to 1 ng/ml prior to GnRH was low on all days studied and was similar for both groups. LH release after GnRH was correlated with increasing days PP in both S (r = .73; P less than .001) and NS (r = .61; P less than .002) cows, Releasable FSH was not related to days PP in either group. Mean peak LH and total LH released were greater (P less than .025 and P less than .05), respectively) in S than in NS cows at 30 d PP. Mean peak FSH and total FSH released were greater (P less than .05 and P less than .07, respectively) at 10 and 30 d PP in S cows than in NS cows. Pre-treatment E, but no P, LH or FSH was positively related (P less than .01) to GnRH-mediated LH release in both groups. When pre-treatment E was partitioned into separated regressions for S (ES) and NS (ENS) cows, increased pituitary LH response in S cows on d 30 appeared to be due in part to a greater sensitivity of S cows to E modulation. We found no evidence to suggest that pituitary responsiveness per se is decreased in beef cows suckling a single calf.
    [Abstract] [Full Text] [Related] [New Search]