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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0574v1 86/6/1335    most recent 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 HighWire Google Scholar Articles by Flores, R. Articles by Rosenkrans, C. F. PubMed PubMed Citation Articles by Flores, R. Articles by Rosenkrans, C. F., Jr

Endocrine factors and ovarian follicles are influenced by body condition and somatotropin in postpartum beef cows^1,2

R. Flores^*, M. L. Looper^,3, R. W. Rorie^*, D. M. Hallford and C. F. Rosenkrans, Jr^*

^* Department of Animal Science, University of Arkansas, Fayetteville, 72701; and USDA-ARS, Dale Bumpers Small Farms Research Center, Booneville, AR 72927; and and Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003

³ Corresponding author: mike.looper{at}ars.usda.gov

Multiparous beef (1/4 to 3/8 Bos indicus; n = 99) cows were managed to achieve low (BCS = 4.3 ± 0.1; n = 50) or moderate (BCS = 6.1 ± 0.1; n = 49) body condition (BC) to determine the influence of bovine (b) ST on the number of follicles, diameter of largest follicle, and serum concentrations of IGF-I, triiodothy-ronine (T3), thyroxine (T4), and prolactin. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST-treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg, s.c.) on d 32, 46, and 60 postpartum. On d 60, all cows received a controlled internal drug-releasing (CIDR) device for 7 d and PGF₂ at CIDR removal (CIDR-PGF₂). Blood samples (7 mL) were collected at each bST treatment and d 39 and 67 postpartum. Ultrasound was performed 1 d after CIDR-PGF₂ to determine the number of small (2 to 9 mm) and large (10 mm) follicles and the diameter of largest follicle. Cows treated with bST in low BC had increased (P < 0.05) IGF-I vs. low-BC non-bST-treated cows on d 39, 46, 60, and 67 postpartum. Prolactin and T3 were greater (P < 0.05) in moderate-BC than in low-BC cows on all sample dates. Thyroxine was greater (P < 0.001) in moderate-BC cows on d 46, 60, and 67 compared with low-BC cows. On d 67, bST-treated cows had greater (P < 0.05) T4 compared with non-bST-treated cows. Diameter of the largest follicle 1 d after CIDR-PGF₂ was greater (P < 0.01) in anestrous cows treated with bST than for non-bST-treated anestrous cows. Diameter of the largest follicle was correlated with concentrations of IGF-I (r 0.18; P 0.08), T3 (r 0.17; P 0.10), and prolactin (r 0.20; P 0.06). Treatment with bST increased IGF-I in low-BC cows, and IGF-I was correlated with the diameter of the largest follicle 1 d after CIDR-PGF₂. Undernutrition of cattle may be communicated to the hypothalamic-pituitary-ovarian axis via metabolic hormones including IGF-I, thyroid hormones, or prolactin.

Key Words: beef cow • body condition • follicle • insulin-like growth factor-I • somatotropin • thyroid hormone

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