title: Energy and protein requirements for growth of Holstein × Gyr heifers.
abstract: There is little information regarding the nutritional requirements for dairy heifers, leading the majority of nutrient requirement systems to consider dairy heifers to be similar to beef heifers. Therefore, we evaluated the muscle protein metabolism and physical and chemical body composition of growing Holstein × Gyr heifers and estimated the energy and protein requirements. We performed a comparative slaughter experiment with 20 Holstein × Gyr heifers at an initial body weight of 218 ± 36.5 kg and an average age of 12 ± 1.0 months. Four heifers were designated as the reference group, and the 16 remaining heifers were fed ad libitum. The 16 heifers were distributed using a completely randomized design in a 2 × 2 factorial arrangement with two roughages (corn silage or sugarcane) and two concentrate levels (30 or 50%) for 112 days. Greater (p < 0.05) values for fractional rates of muscle protein synthesis, degradation and accretion were observed for heifers that were fed 50% concentrate. The following equations were obtained to estimate the net energy for gain (NEg) and net protein for gain (NPg): NEg(Mcal/day) = 0.0685 × EBW0.75× EBWG1.095and NPg(g/day) = 203.8 × EBWG - 14.80 × RE, respectively, in which EBW is the empty body weight, EBWG is the empty body weight gain and RE is the retained energy. We concluded that increased rates of protein turnover are achieved when a greater quality diet is provided. In the future, these results can be used to calculate the nutritional requirements for growth of Holstein × Gyr heifers after equation validation rather than using the recommendations provided by other systems, which use values developed from beef heifers, to determine the nutritional requirements of dairy cattle.
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: F A S
authors.initials: FAS
authors.lastname: Silva
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: S C
authors.initials: SC
authors.lastname: Valadares Filho
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: L N
authors.initials: LN
authors.lastname: Rennó
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: D
authors.initials: D
authors.lastname: Zanetti
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: L F
authors.initials: LF
authors.lastname: Costa E Silva
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: L A
authors.initials: LA
authors.lastname: Godoi
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: J M P
authors.initials: JMP
authors.lastname: Vieira
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: A C B
authors.initials: ACB
authors.lastname: Menezes
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: P
authors.initials: P
authors.lastname: Pucetti
authors.affiliation: Animal Science Department, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
authors.forename: P P
authors.initials: PP
authors.lastname: Rotta
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000254:growth & development*; D004032:Diet / Q000662:veterinary*; D004044:Dietary Proteins / Q000008:administration & dosage*; D002149:Energy Intake; D005260:Female; D009124:Muscle Proteins / Q000378:metabolism; D009751:Nutritional Requirements; D031786:Saccharum; D012820:Silage / Q000032:analysis; D003313:Zea mays
chemical_list: D004044:Dietary Proteins; D009124:Muscle Proteins
keywords: comparative slaughter; protein turnover; sugarcane; tissue deposition