title: Mammary gland development of dairy heifers fed diets containing increasing levels of metabolisable protein: metabolisable energy.
abstract: This study was conducted to evaluate the development of the mammary gland in Holstein heifers subjected to different dietary metabolisable protein (MP): metabolisable energy (ME) ratios. Twenty-five Holstein heifers (initial body weight (BW) 213±13·5 kg and initial average age 7·8±0·5 months) were divided into five treatments. The treatments were designed to provide MP:ME ratios equal to 33, 38, 43, 48, and 53 g of MP per Mcal of ME. All diets were formulated to have the same energy content (2·6 Mcal ME/kg dry matter). Actual MP:ME ratios were 36·2, 40·2, 46·2, 47·1, and 50·8 g MP/Mcal ME. The experiment was conducted in a randomised block design, while considering initial BW as a blocking factor to evaluate pre- and post-pubertal periods. Block effect was not observed for all variables evaluated; hence it was considered that the diets had the same influence both on pre- and post-pubertal phases. Dry matter and nutrient intake did not change between treatments, excepting protein intake and digestibility. Serum concentrations of insulin-like growth factor 1 increased linearly across treatments. Changes in the pixel brightness of mammary gland ultrasound images, which are associated with lipid content, were significantly influenced by MP:ME ratios in the diet of heifers that were subjected to accelerated growth rates. It is not recommended to use diets of less than 38 g MP/Mcal ME in diets to heifers allowed to gain more than 1 kg/d.
authors.affiliation: Animal Science Department,Federal University of Viçosa,Viçosa,Minas Gerais 36571-000,Brazil.
authors.forename: Ronan L
authors.initials: RL
authors.lastname: Albino
authors.affiliation: Animal Science Department,Federal University of Viçosa,Viçosa,Minas Gerais 36571-000,Brazil.
authors.forename: Marcos I
authors.initials: MI
authors.lastname: Marcondes
authors.affiliation: Department of Dairy Science,Virginia Polytechnic Institute and State University,Blacksburg 24061,USA.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Akers
authors.affiliation: Animal Science Department,Federal University of Viçosa,Viçosa,Minas Gerais 36571-000,Brazil.
authors.forename: Edenio
authors.initials: E
authors.lastname: Detmann
authors.affiliation: Embrapa Gado de Leite,Juiz de Fora,Minas Gerais 36038-330,Brazil.
authors.forename: Bruno C
authors.initials: BC
authors.lastname: Carvalho
authors.affiliation: Embrapa Gado de Leite,Juiz de Fora,Minas Gerais 36038-330,Brazil.
authors.forename: Tadeu E
authors.initials: TE
authors.lastname: Silva
mesh_terms: D000821:Animal Feed; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D002149:Energy Intake; D004734:Energy Metabolism; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D008055:Lipids / Q000032:analysis; D008321:Mammary Glands, Animal / Q000737:chemistry / Q000000981:diagnostic imaging / Q000254:growth & development*; D014463:Ultrasonography
chemical_list: D004044:Dietary Proteins; D008055:Lipids; D007334:Insulin-Like Growth Factor I
keywords: Heifer; mammary gland; ultrasound