J. Anim Sci.
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Journal of Animal Science, Vol 72, Issue 9 2425-2430, Copyright © 1994 by American Society of Animal Science

CLINICAL TRIAL

Recombinant bovine somatotropin does not improve superovulatory response in sheep

D. C. Eckery, C. L. Moeller, T. M. Nett and H. R. Sawyer
Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins 80523.

Although treatment of heifers and ewes with recombinant bovine somatotropin (rbST) does not increase ovulation rate, data for heifers indicate that the number of small antral follicles is approximately doubled. Accordingly, the objectives of this study were to determine whether 1) treatment of ewes with rbST would increase the number of small antral follicles, thereby increasing the number of follicles that could potentially respond to superovulation treatment, and 2) superovulatory responses could be improved in ewes with "synchronized" populations of follicles. Twenty-four ewes were divided into four groups: control, control+rbST, hypothalamic-pituitary stalk disconnected (HPD), and HPD+rbST. Beginning on d 5 of the estrous cycle, ewes were injected once daily for 13 d with either rbST (3 mg) or saline. The superovulatory regimen consisted of a single dose of PMSG followed by twice-daily injections of FSH for four consecutive days. After ovariectomy, ovulation sites and follicles were counted. Twice-daily blood samples were assayed for somatotropin (ST) and IGF-I. The concentrations of ST in rbST-treated ewes were greater (P < .05) than those in controls. Treatment with rbST increased (P < .05) the mean serum concentration of IGF-I in control but not in HPD ewes. There was no increase in ovulation rate or number of small antral follicles in response to rbST. Synchronizing follicle populations also failed to increase ovulation rate or reduce variability of response. We conclude that supplementation with rbST and synchronization of follicles does not increase the superovulatory response in sheep.


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L. R. Gentry, D. L. Thompson Jr., G. T. Gentry Jr., K. A. Davis, and R. A. Godke
High versus low body condition in mares: Interactions with responses to somatotropin, GnRH analog, and dexamethasone
J Anim Sci, December 1, 2002; 80(12): 3277 - 3285.
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Copyright © 1994 by the American Society of Animal Science.