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Effects of Whole Cottonseed Diet and Recombinant Bovine Somatotropin on Ovarian Follicles in Lactating Dairy Cows¹

T. Kassa^*,2, J. D. Ambrose^*,3, A. L. Adams^*,4, C. Risco, C. R. Staples^*, M.-J. Thatcher, H. H. Van Horn^*, A. Garcia^*, H. H. Head^* and W. W. Thatcher^*

^* Department of Animal Sciences, Institute for Food and Agricultural Sciences and
College of Veterinary Medicine, University of Florida, Gainesville 32611

Corresponding author:
W. W. Thatcher; e-mail:
thatcher{at}animal.ufl.edu.

The effects of whole cottonseed (WCS) in the diet and the administration of bovine somatotropin (bST) on ovarian follicular dynamics and plasma progesterone (P₄) concentrations were examined in cows during a period of synchronized follicular growth. Lactating Holstein cows (n = 28) were randomly assigned to treatments in a 2 x 2 factorial arrangement. Diets consisted of WCS (15% of dry matter) or no WCS, and bST at a dose of 0 or 208 mg/14 d. Dietary treatments began within 24 h of calving and bST treatments began within 7 d postpartum. Cows received GnRH at 65 ± 3 d postpartum (d 0), PGF₂ (d 7), a second dose of GnRH (d 9), and were inseminated 16 h later (d 10). Ovarian changes were monitored daily by ultrasonography from d 0 to 9. On d 9, 93% of cows had a preovulatory follicle and 86% ovulated. For Class 2 (6 to 9 mm) follicles, a diet x bST interaction was detected, with bST stimulating Class 2 follicles in cows fed WCS, but not in cows on the control diet. Neither diet nor bST affected numbers of Class 1 (2 to 5 mm) or Class 3 (10 mm) follicles or sizes of the subordinate and dominant follicles. During the luteal phase of the cycle, lactating cows fed WCS tended to have elevated concentrations of plasma P₄, whereas bST was without effect. Plasma concentrations of high-density lipoprotein cholesterol were increased in cows fed WCS. Number and diameter of corpora lutea did not differ among treatments.

Key Words: dairy cow • follicle • somatotropin • whole cottonseeds

Abbreviation key: CL = corpus luteum, HDL = High density lipoprotein cholesterol, P₄ = progesterone, WCS = whole cottonseed

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