Abstract
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.
Highlights
The global scientific research on animal nutrition has tried to define the nutrients required by the animals, for more than a century (Preston, 2006)
The average ratio between empty body weight (EBW) and heat production (HP) was 0.914 superior to those reported by BR-CORTE (Valadares Filho et al, 2010) and the NRC (2000), which were 0.895 and 0.891, respectively
For the conversion of requirements for empty body weight gain (EBG) into requirements of average body weight daily gain (ADG), the average ratio between EBWG and average daily gain (ADG) was 1.013, which was very close to the 1.014 of noncastrated Nellore finishing cattle (Marcondes et al, 2007) and 8.6 and 7.2% higher than those obtained by Valadares Filho et al (2010) and the NRC (2000), who and which presented EBWG/ADG ratios of 0.936 and 0.951, respectively
Summary
The global scientific research on animal nutrition has tried to define the nutrients required by the animals, for more than a century (Preston, 2006). Knowing the concentration of the amount of nutrients in the diet that each animal category requires to achieve the desired performance, along with knowledge of the nutritional value of the feedstuffs available, allows us to efficiently, technically and economically formulate diets, plan and implement the nutritional management of the herd (Valadares Filho & Chizzotti, 2011). Valadares Filho et al (2006) published the first Brazilian charts of nutritional requirements of Zebu cattle. They were formulated from a relatively small database. Valadares Filho et al (2010) published the Brazilian Tables of Nutritional Requirements of Zebu Beef Cattle (BR-CORTE, 2nd edition), using a database with experiments conducted in Brazilian conditions in the last two decades. The majority of the animals on the database utilized were in the finishing phase (Chizzotti et al, 2007; Marcondes et al, 2009; Souza et al, 2009)
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