title: Induction of precocious puberty in heifers III: hastened reduction of estradiol negative feedback on secretion of luteinizing hormone.
abstract: Precocious puberty (<300 d of age) can be induced in beef heifers by early weaning and feeding a high-concentrate diet. The objective of this experiment was to determine whether precocious puberty occurs as a result of a hastened reduction of estradiol negative feedback on secretion of LH. Thirty crossbred Angus and Simmental heifers were weaned at 83 +/- 2 d of age and 114 +/- 3 kg of BW, blocked by BW, and randomly assigned to receive a high-concentrate (60% corn; H) or control (30% corn; C) diet and to receive ovariectomy (OVX), OVX plus an estradiol implant (OVXE), or to remain intact (INT). Residual ovarian tissue after OVX necessitated withdrawal of 6 heifers during the course of the experiment, resulting in the following treatment groups: OVX-C, n = 3; OVX-H, n = 5; OVXE-C, n = 4; OVXE-H, n = 2; INT-C, n = 5; INT-H, n = 5. To determine concentrations of progesterone and estradiol, blood samples were collected weekly beginning at a mean age of 160 d. To characterize LH concentrations, serial blood samples were collected at 12-min intervals for 12 h at mean ages of 119, 149, 188, 217, 246, 281, 323, 365, 407, and 449 d. By a mean age of 202 d, heifers fed the H diet were heavier (P < 0.05) than those fed the C diet. Heifers in the INT-H treatment attained puberty earlier (P < 0.05) than in the INT-C treatment (275 +/- 30 vs. 385 +/- 14 d of age, respectively). Overall mean concentrations of estradiol did not differ between OVXE-H and OVXE-C, between INT-H and INT-C, or between OVXE and INT treatments. The OVX treatments exhibited greater LH pulse frequency than the OVXE and INT treatments by the first serial blood collection (treatment x age, P < 0.05). The frequency of LH pulses was greater (P < 0.05) in the INT-H than the INT-C treatment by a mean age of 246 d and was greater (P < 0.05) in the OVXE-H than the OVXE-C treatment by a mean age of 281 d. In the OVXE-H treatment, LH secretion increased and subsequently "escaped" from estradiol negative feedback (detection of > or = 1 LH pulse/h) earlier (P < 0.05) than in the OVXE-C treatment (307 +/- 30 and 420 +/- 21 d of age, respectively). It is concluded that advancing the reduction of estradiol negative feedback on secretion of LH is the mechanism by which early weaning and feeding a high-concentrate diet results in precocious puberty in heifers.
authors.affiliation: Department of Animal Sciences, The Ohio State University, Columbus 43210, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Gasser
authors.forename: G A
authors.initials: GA
authors.lastname: Bridges
authors.forename: M L
authors.initials: ML
authors.lastname: Mussard
authors.forename: D E
authors.initials: DE
authors.lastname: Grum
authors.forename: J E
authors.initials: JE
authors.lastname: Kinder
authors.forename: M L
authors.initials: ML
authors.lastname: Day
mesh_terms: D000375:Aging; D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood* / Q000378:metabolism*; D010052:Ovariectomy / Q000662:veterinary; D012741:Sexual Maturation / Q000187:drug effects*; D015430:Weight Gain / Q000187:drug effects; D003313:Zea mays
chemical_list: D004040:Dietary Carbohydrates; D004958:Estradiol; D007986:Luteinizing Hormone