P. P. Rotta

Macrominerals and Trace Element Requirements for Beef Cattle

Eighty-seven Nellore animals were utilized in this study to estimate net requirements for the maintenance and growth of beef cattle as well as the retention coefficients of 13 minerals: macrominerals (Ca, P, Mg, K, Na, and S) and trace elements (Cu, Fe, Mn, Se, Zn, Co, and Cr). The net requirements for maintenance and the true retention coefficient were estimated by using the regression between apparent retention and intake for each mineral. The net requirement for maintenance (μg/kg BW) and retention coefficients (%) were 163 and 85 for Cu, 2,097 and 53 for Fe, 32.3 and 24 for Mn, 3.72 and 48 for Se, 669 and 0.80 for Zn, 18.4 and 86 for Co, and 22.9 and 78 for Cr. The dietary requirements of macrominerals (g/kg DMI) were 5.12 for Ca, 2.38 for P, 0.96 for Mg, 2.40 for K, 0.79 for Na, and 1.47 for S. This is the first study using Nellore cattle to estimate mineral requirements; considering that Nellore cattle are the most common breed in Brazil and that Brazil is a major beef producer globally, this knowledge can help producers to improve animal performance by supplying the correct amount of minerals.

Energy and protein nutritional requirements for Nellore bulls

The objective of this study was to determine the nutritional requirements of energy and protein and estimate the efficiencies of metabolizable energy utilization for fat and protein deposition, as well as for maintenance (km) and growth (kg). An experiment of comparative slaughter was carried out with thirty-seven 14-month-old (±1 month) Nellore bulls with 259±24.9 kg. Animals were divided as follows: five to reference, four to maintenance level and twenty-eight bulls feeding ad libitum. Bulls were also grouped in 4 different feedlot periods (42, 84, 126 and 168 days) for slaughter. The diet was composed of corn silage and concentrate, at a 55:45 ratio. After the slaughter, the left half carcasses were totally dissected for determination of body composition. The energy requirements for maintenance were obtained by exponentially relating the heat production and the metabolizable energy intake, while the energy requirements for gain (NEg) were obtained according to empty body weight (EBW) and EBW gain (EBG). The net protein requirements for gain (NPg) were estimated according to EBG and retained energy (RE). The net (NEm) and metabolizable (MEm) energy requirements for maintenance were 76.5 and 113.84 kcal/EBW0.75/day, respectively. The km was 0.67. The equations for NEg and NPg were: NEg (Mcal/day) = 0.0555 × EBW0.75 × EBG1.095 and NPg (g/day) = 263.37 × EBG - 23.21 × RE. The kg was 0.33. The efficiencies to deposition of energy as protein and fat were 0.18 and 0.71, respectively. The model obtained for the percentage of retained energy as protein (%REp) was %REp = 2.4221 × (RE/EBG)-1.6472. The net and metabolizable energy requirements for maintenance of Nellore bulls were 76.5 and 113.84 kcal/EBW0.75/day. The energy and protein requirements for gain could be obtained by the respective equations: NEg (Mcal/day) = 0.0555 × EBW0.75 × EBG1.095 and NPg (g/day) = 263.37 × EBG - 23.21 × RE.