title: Endocrine factors and ovarian follicles are influenced by body condition and somatotropin in postpartum beef cows.
abstract: 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 PGF(2alpha) at CIDR removal (CIDR-PGF(2alpha)). Blood samples (7 mL) were collected at each bST treatment and d 39 and 67 postpartum. Ultrasound was performed 1 d after CIDR-PGF(2alpha) 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-PGF(2alpha) 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-PGF(2alpha). Undernutrition of cattle may be communicated to the hypothalamic-pituitary-ovarian axis via metabolic hormones including IGF-I, thyroid hormones, or prolactin.
authors.affiliation: Department of Animal Science, University of Arkansas, Fayetteville 72701, USA.
authors.forename: R
authors.initials: R
authors.lastname: Flores
authors.forename: M L
authors.initials: ML
authors.lastname: Looper
authors.forename: R W
authors.initials: RW
authors.lastname: Rorie
authors.forename: D M
authors.initials: DM
authors.lastname: Hallford
authors.forename: C F
authors.initials: CF
authors.lastname: Rosenkrans
mesh_terms: D000818:Animals; D001823:Body Composition / Q000502:physiology*; D001824:Body Constitution / Q000502:physiology; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D009752:Nutritional Status; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000502:physiology*; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology*; D049590:Postpartum Period / Q000097:blood; D011247:Pregnancy; D011388:Prolactin / Q000097:blood; D011897:Random Allocation; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014463:Ultrasonography
chemical_list: D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D013006:Growth Hormone; D015237:Dinoprost; D013974:Thyroxine