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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 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

This article has been cited by other articles:

				M. L. Looper, S. G. Black, S. T. Reiter, R. Okimoto, Z. B. Johnson, M. A. Brown, and C. F. Rosenkrans Jr. Identification of Polymorphisms in the Enhancer Region of the Bovine Prolactin Gene and Association with Profitability Traits of Beef Cattle Professional Animal Scientist, February 1, 2010; 26(1): 103 - 108. [Abstract] [PDF]

				C. A. Lents, F. J. White, N. H. Ciccioli, R. P. Wettemann, L. J. Spicer, and D. L. Lalman Effects of body condition score at parturition and postpartum protein supplementation on estrous behavior and size of the dominant follicle in beef cows J Anim Sci, October 1, 2008; 86(10): 2549 - 2556. [Abstract] [Full Text] [PDF]