Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2008
Publication Date: 3/1/2008
Citation: Looper, M.L., Flores, R., Rorie, R.W., Hallford, D.M., Rosenkrans, C.F. 2008. Endocrine and follicular dynamics are influenced by body condition and somatotropin in post-partum beef cows. Journal of Animal Science. 86:1335-1344.
Interpretive Summary: A 10% increase in the annual U.S. calf crop would allow production of the same amount of beef from 12% fewer cows. Thin beef cattle do not get pregnant at the end of the breeding season reducing profitability of beef production. The hormonal signals by which the brain and the ovary communicate in the cow are not fully understood. Scientists from ARS in Booneville, AR, and University of Arkasnas and New Mexico State University personnel investigated the effects of bovine somatotropin (bST) and body condition on the number of ovarian follicle, and serum concentrations of hormones in beef cows. Thin cows had reduced concentrations of all hormones and smaller ovarian follicles. Treatment of thin cows with bST increased the size of ovarian follicles and increased hormones important to cow reproduction. Knowledge of what hormones are affected by nutrition may aide beef producers in increasing the number of pregnant cows in their herd. This information is important to livestock producers and extension personnel.
Technical Abstract: Ninety-nine, multiparous beef cows were managed to achieve low (body condition score = 4.3 ± 0.1; n = 50) or moderate (body condition score 6.1 ± 0.1; n = 49) body condition (BC) to determine the influence of bovine somatotropin (bST) on number of follicles, diameter of largest follicle, and serum concentrations of insulin-like growth factor-I (IGFI), triiodothyronine (T3), thyroxine (T4), and prolactin. Beginning 32 days postpartum, cows within each BC were assigned randomly to treatment with or without bST. Control cows received no bST treatment and treated cows were administered bST (Posilac, 500 mg, s.c.) on day 32, 46, and 60 postpartum. On day 60, all cows received a controlled internal drugreleasing (CIDR; 1.38 g progesterone) device for 7 days and prostaglandin F2alpha (PGF; 25 mg i.m.) at CIDR removal. Blood samples were collected at each bST treatment and day 39 and 67 postpartum. Ultrasound was performed 1 day after CIDR-PGF to determine number of small (2 to 9 mm) and large ( 10 mm) ovarian follicles, and diameter of largest ovarian follicle. Cows treated with bST in low BC had increased IGF-I vs. control-low BC cows on day 39, 46, 60, and 67 postpartum. Prolactin and T3 were greater in moderate BC than low BC cows. Thyroxine was greater in moderate BC cows on day 39, 46, 60, and 67 postpartum compared with low BC cows. On day 39 and 67, bST-treated cows had greater T4 compared with control cows. Diameter of the largest follicle tended to be smallest for control-low BC cows. Diameter of largest follicle was correlated with concentrations of IGF-I, T3, and prolactin. Somatotropin and BC may influence follicular dynamics of cattle via IGF-I, thyroid hormones, and (or) prolactin.