Nutrient requirements and evaluation of equations to predict chemical body composition of dairy crossbred steers

Abstract

Objective: Objectives were to estimate energy and protein requirements of dairy crossbred steers, as well as to evaluate equations previously described in the literature (HH46 and CS16) to predict the carcass and empty body chemical composition of crossbred dairy cattle.Methods: Thirty-three Holstein × Zebu steers, aged 19 ± 1 months old, with an initial shrunk body weight of 324 ± 7.7 kg, were randomly divided into three groups: reference group (n = 5), maintenance level (1.17% BW; n = 4), and the remaining 24 steers were randomly allocated to 1 of 4 treatments. Treatments were: intake restricted to 85% of <i>ad libitum</i> feed intake for either 0, 28, 42, or 84 d of an 84-d finishing period.Results: The net energy and the metabolizable protein requirements for maintenance were 0.083 Mcal/EBW^0.75/d and 4.40 g/EBW^0.75, respectively. The net energy (NE_G) and protein (NP_G) requirements for growth can be estimated with the following equations: NE_G (Mcal/kg EBG) = 0.2973_{(± 0.1212)} × <i>EBW</i>^{0.4336(± 0.1002)} and NP_G (g/d) = 183.6_{(± 22.5333)} × EBG – 2.0693_{(± 4.7254)} × RE, where EBW = empty body weight, EBG = empty body gain, and RE = retained energy. Crude protein (CP) and ether extract (EE) chemical contents in carcass, and all the chemical components in the empty body were precisely and accurately estimated by CS16 equations. However, water content in carcass was better predicted by HH46 equation.Conclusion: The equations proposed in this study can be used for estimating the energy and protein requirements of crossbred dairy steers. The CS16 equations were the best estimator for CP and EE chemical contents in carcass, and all chemical components in the empty body of crossbred dairy steers, whereas water in carcass was better estimated using the HH46 equations.