Nitrogen balance and nutrient requirements of young Nellore bulls fed with static or oscillating crude protein levels, and feeding behavior, water intake and requirements of bulls with different residual feed intakes

• Ano de defesa: 2019
• Autor(a) principal: Menezes, Ana Clara Baião
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Nelore (Bovino) - Nutrição; Nutrição - Necessidades; Nitrogênio na nutrição animal; Consumo alimentar; Nutrição e Alimentação Animal
• Link de acesso: https://locus.ufv.br//handle/123456789/27539

Our objectives with this study were 1) to evaluate the effects of dietary crude protein (CP) supply on intake, digestibility, performance, N balance, and requirements of young Nellore bulls, and 2) to determine feeding behavior, water intake, and requirements of high and low residual feed intake (RFI) Nellore bulls. 42 young bulls (initial BW of 260 ± 8.1 kg; age of 7 ± 1.0 mo) were fed ad libitum and were randomly assigned to receive one of six diets with different CP concentrations for 140 d: 105 (LO), 125 (MD), or 145 g CP /kg DM (HI), and LO to HI (LH), LO to MD (LM), or MD to HI (MH) oscillating CP at a 48-h interval for each feed. The bulls were housed in a feedlot in group pens that contained electronic feeders, waterers, and a scale connected to the waterers. At the end of the experiment, bulls were slaughtered to evaluate carcass characteristics. There was no alteration in the performance of growing Nellore bulls fed with oscillating CP diets versus a static level of 125 g CP/kg DM, nor static LO and HI levels; however, there may be undesirable increases in environmental N excretion when the average dietary CP content is increased. The results suggest that dietary CP concentrations of 105, 125 g/kg DM, or within this range can be indicated for finishing young Nellore bulls, since it reaches the requirements, reduces the environmental footprint related to N excretion, and may save on costs of high-priced protein feeds. Regarding requirements, the net energy requirements for maintenance and metabolizable energy (ME) for maintenance were 77 and 122.75 Kcal/EBW0.75/d, respectively. The efficiency of ME utilization for maintenance was 62.7%. The equation obtained for net energy for gain (NEg) was: NEg (Mcal/EBW0.75/d) = 0.0535 × EBW0.75 × EBG0.7131, where EBG is the empty body gain, and the efficiency was 24.25%. Net protein for gain (NPg) was: NPg (g/d) = 227.372 × EBG – 19.479 × RE. There was a linear increase for carcass, CP, and water present in the EBW as the animal grew. The EE deposition exponentially increased as EBW increased. Low RFI bulls had lower DMI intake than high RFI bulls, and no differences were observed between the two groups regarding performance and feeding behavior measurements. The net energy requirements for maintenance, metabolizable energy for maintenance, and efficiency of metabolizable energy utilization were 63.4, 98.6 kcal/EBW0.75/d, and 64.3%, respectively for low RFI bulls, and 78.1, 123.9 kcal/EBW0.75/d, and 63.0% for high RFI bulls. We did not observe any difference regarding the composition of gain in terms of protein or fat deposition between the two groups. Both groups presented also similar carcass and non-carcass traits. Therefore, our study shows that low RFI Nellore bulls eat less, grow at a similar rate, and have lower maintenance energy requirements than high RFI bulls. We also suggest that the lower feed intake did not compromises the carcass traits of more efficient animals, which would reduce production costs and increase the competitiveness of the Brazilian beef sector on the world market. Keywords: Nellore. Nitrogen. Performance. Requirements. Residual Feed Intake.