title: Growth, intake, and health of Holstein heifer calves fed an enhanced preweaning diet with or without postweaning exogenous estrogen.
abstract: Research has shown that changes in nutrition both before and after weaning can affect mammary development. Additionally, estrogen is known to be a potent mammogenic stimulant. Our objectives were to determine effects of altered preweaning feeding and exogenous estradiol postweaning on growth, intake, and health. Thirty-six Holstein heifer calves were reared on (1) a restricted milk replacer (MR) diet fed at 0.44kg powder dry matter (DM)/day [R; 20.9% crude protein (CP), 19.8% fat, DM basis], or (2) an enhanced MR fed at 1.08kg powder DM/d (EH; 28.9% CP, 26.2% fat, DM basis). The MR feeding was reduced 50% during wk 8 to prepare for weaning. Starter was offered after wk 4 but balanced between treatments. Body weight and frame were measured weekly with intakes and health monitored daily. At weaning, a subset of calves were slaughtered (n=6/diet). Enhanced-fed calves had greater carcass, thymus, liver, spleen, and mammary gland (parenchyma and mammary fat pad) weights. The EH calves also had greater average daily gain (ADG) starting during wk 1 (0.36 vs. -0.06kg/d) and lasting through wk 7 (1.00 vs. 0.41kg/d). Remaining calves received estrogen implants or placebo and were slaughtered at the end of wk 10, creating 4 treatments: (1) R, (2) R + estrogen (R-E2), (3) EH, and (4) EH + estrogen (EH-E2). Postweaning ADG was similar between R, EH, and EH-E2 calves, but greater in R-E2 calves than E calves. The EH-E2 calves had the heaviest mammary glands, and R-E2 calves had heavier mammary glands than R calves. The EH calves consumed more MR DM, CP, and fat preweaning. The R-fed calves consumed more starter DM preweaning. Fecal score was greater for EH calves (1.74 vs. 1.50) preweaning, but days medicated did not differ. Fecal scores were lower for R-E2 calves postweaning. Improved preweaning feeding of calves increased body weights and frame measures. Differences in body weights remained postweaning. Enhanced-fed calves showed greater ADG during the preweaning period but not postweaning. Exogenous estrogen may elicit diet-dependent growth responses. Analysis of collected samples will allow determination of cellular and molecular processes responsible for the marked differences in mammary development observed.
authors.affiliation: Department of Dairy Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061.
authors.forename: A J
authors.initials: AJ
authors.lastname: Geiger
authors.affiliation: Department of Dairy Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061.
authors.forename: C L M
authors.initials: CLM
authors.lastname: Parsons
authors.affiliation: Department of Dairy Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061.
authors.forename: R E
authors.initials: RE
authors.lastname: James
authors.affiliation: Department of Dairy Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061. Electronic address: rma@vt.edu.
authors.forename: R M
authors.initials: RM
authors.lastname: Akers
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D008321:Mammary Glands, Animal / Q000254:growth & development; D009752:Nutritional Status; D011897:Random Allocation; D014886:Weaning
chemical_list: D004958:Estradiol
keywords: calf; estradiol; mammary gland; milk replacer