title: Effect of dietary energy on milk production and metabolic hormones in thin, primiparous beef heifers.
abstract: Thirty-six primiparous heifers were used to determine the effect of dietary energy on postpartum interval, milk production, serum concentrations of insulin, insulin-like growth factor I (IGF-I), growth hormone, and cerebrospinal fluid (CSF) concentrations of neuropeptide-Y (NPY). Low-quality hay was fed during the last trimester of pregnancy to achieve suboptimal calving weight (370 +/- 5 kg) and condition score (4.0 +/- .1). After calving, cows were allotted to one of four dietary treatments that differed in metabolizable energy. Experimental diets were fed at 2.5% of shrunk body weight and formulated to provide 1.8 (low), 2.1 (maintenance), 2.4 (maintenance high), or 2.7 (high) Mcal of ME/kg DM. Daily milk production was estimated at approximately 30, 60, and 90 d postpartum. Condition score change and weight change were defined as change from calving to d 90 postpartum. As energy intake increased, condition score change (P < .001), IGF-I (P < .001) and insulin (P < .01) increased and postpartum interval decreased (P = .04). No relationship existed between postpartum interval and CSF concentration of NPY (P > .1). Condition score change was positively associated with IGF-I and insulin (r = .71, P < .001; r = .38, P = .02, respectively) and negatively associated with GH (r = -.67, P < .001). Weight change and serum concentrations of GH did not differ (P > .10) among treatments. Increasing dietary energy intake was associated with a curvilinear increase in milk yield (P = .04) and percentage milk fat (P = .03) and a linear increase (P = .04) in energy available for milk production. Greater milk yield at d 30 was associated with a longer postpartum interval (r = .34, P < .05). In conclusion, a greater proportion of net energy is partitioned to maternal tissue realimentation when cows receive high compared to low-, maintenance-, or moderate-energy diets.
authors.affiliation: Department of Animal Sciences, Oklahoma State University, Stillwater 74078, USA. dlalman@okstate.edu
authors.forename: D L
authors.initials: DL
authors.lastname: Lalman
authors.forename: J E
authors.initials: JE
authors.lastname: Williams
authors.forename: B W
authors.initials: BW
authors.lastname: Hess
authors.forename: M G
authors.initials: MG
authors.lastname: Thomas
authors.forename: D H
authors.initials: DH
authors.lastname: Keisler
mesh_terms: D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000097:blood / Q000502:physiology*; D004734:Energy Metabolism; D005260:Female; D013006:Growth Hormone / Q000097:blood; D006706:Homeostasis; D007328:Insulin / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D007774:Lactation; D009478:Neuropeptide Y / Q000097:blood; D009479:Neuropeptides / Q000097:blood*; D010298:Parity; D011247:Pregnancy
chemical_list: D007328:Insulin; D009478:Neuropeptide Y; D009479:Neuropeptides; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone