Desempenho e exigências nutricionais de novilhos zebuínos sob pastejo

• Ano de defesa: 2008
• Autor(a) principal: Sales, Maykel Franklin Lima
• Orientador(a): Paulino, Mário Fonseca
• Banca de defesa: Paulino, Pedro Veiga Rodrigues , Henriques, Lara Toledo , Zervoudakis, Joanis Tilemahos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Energia; Gado de corte; Minerais; Proteína; Suplementação
• Palavras-chave em Inglês: Energy; Beef cattle; Minerals; Protein; Supplementation
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::NUTRICAO E ALIMENTACAO ANIMAL
• Link de acesso: http://locus.ufv.br/handle/123456789/1706

The current thesis was based on three trials. At the first trial, it was evaluated the effects of different supplementation levels on the performance, intake, digestibility, pH and ruminal ammonia concentration in growing bulls grazing Brachiaria decumbens Stapf. pasture, during the dry-rainy transition season. In the performance, intake and digestibility trial twenty five intact males with 11 months old and initial body weight of 270 kg, grouped in five lots of five animals, arranged in a completely randomized design were used. Each lot received one of the following treatments: mineral mixture (SAL) or supplements fed at 0.5, 1.0, 1.5 or 2.0 kg/animal/ day, which corresponded to supplementation levels of 0.18, 0.36, 0.54 and 0.72% of body weight. The experimental area was constituted of five paddocks of 2.0 ha each one. For the evaluation of the pH and ruminal ammonia concentration five crossbred bulls were used, with average body weight of 240 kg, fitted with esophageal, ruminal and abomasal cannula, disposed in a 5x5 Latin square design, with five treatments and five experimental periods. Animal performance increased linearly with the supplementation levels, being observed an increment of more than 80% in the animal performance of the highest supplementation level when compared to the animals that not receive the supplement. DM, OM and NDF intake were not influenced by the treatments. CP, NFC, EE and TDN intake as well as nutrient digestibility and ruminal ammonia concentration had a positive linear pattern in function of the supplementation levels. Increasing the amount of supplemental concentrate had a positive influence on the performance of growing bulls grazing Brachiaria decumbens pasture during the dry-rainy transition season. At the second trial it was evaluated the effects of supplementation levels on performance, intake, total apparent digestibility (TAD), pH and ruminal ammonia concentration (RAC) of finishing bulls grazing Brachiaria decumbens Stapf. pasture during the rainy season. For the performance, intake and TAD evaluation, sixteen intact males with 14 months old and initial body weight of 317 kg were used, arranged into four lots of four animals each, following a completely randomized design. Each lot received one of the following treatments: mineral mixture or supplements fed at 0.75; 1.50 and 2.25 kg/animal/day, which corresponded supplementation levels of 0.2; 0.4 and 0.6% of the average body weight. For pH and RAC evaluation, four animals fitted with rumen cannula were used, following a 4 x 4 Latin square design, with four treatments and four experimental periods. The average daily gain increased linearly as the supplementation levels increased, when the animals fed at the higher supplementation level presenting an additional daily gain of 261 g/day when compared to the animals not supplemented. DM, OM, CP, NFC, EE and TDN intake had a positive and linear response to the treatments. Although the treatments had no effect on DM TAD, there was a significant effect on nutrients TAD, in which the response was positive and linear for OM, CP, EE and NFC and linear but negative for NDF TAD. Ruminal pH values were affected quadratically while RAC increased linearly with the supplementation levels. Increasing supplementation levels can positively influence the performance, intake, nutrients digestibility and ruminal characteristics of bulls grazing Brachiaria decumbens during the rainy season. The objective in the third trial was to determine the energy, protein and macrominarals requirements of Zebu bulls grazing Brachiaria decumbens Stapf. pasture and supplemented with increasing amounts of concentrate during the rainy season. Twenty eight intact males, with seven months old and initial body weight of 180 kg were used. Eight baseline animals were slaughtered to determine the initial body composition, in different weight range. The right half carcass of eight animals, two per treatment, was dissected in muscle, fat and bones and all the body components were weighed to determine the empty body weight (EBW) and empty body composition. The net energy requirements for weight gain were obtained by regressing the log of the retained energy (RE) on the log of empty body weight gain (EBWG). The net energy requirements for maintenance (NEm) were obtained from regression of the log of the heat production (HP) on the metabolizable energy intake (MEI). The efficiency of ME utilization for maintenance (km) was calculated as the ratio of NEm to MEm and the slope of the linear regression of RE on ME intake was considered as an estimate of the efficiency of utilization of ME for weight gain (kg). The requirements of NEm of Zebu bulls, under pasture, was 82.4 kcal/EBW0.75/day or 76.12 kcal/BW0.75/day. Thus, grazing Zebu bulls have about 5% greater net energy requirements for maintencance than feedlot Zebu bulls. The daily requirements of MEm was 149.76 kcal/EBW0.75, and the efficiency of ME utilization for maintenance (km) of Zebu bulls under pasture was 55% and for gain (kg) 29%. To calculate the net requirements for gain in the different ranges of body weight the retained protein (RP, g/day) was regressed against empty body gain (EBG, kg/day) and retained energy (RE, Mcal/day). The total metabolizable protein requirements for an animal of 350 kg and average daily gain of 1.0 kg, were 593.59 g/day. That same animal, eating 7.40 kg of DM/day requires 12.97% of CP in DM. The net requirements of protein for gain of grazing bulls until 350 kg of bodyweight, decrease as the body weight or retained energy increase and can be estimated by the equation: RP (g/day) = -26.2946+247.4853×EBG-24.8436 ×RE. The net Ca, P, Mg, Na and K requirements were determined by the equation Y = b. 10a. Xb-1, where a and b represente the intercept and the regression coefficient, respectively, of the prediction equations of Ca, P, Mg, Na or K contents in the empty body weight. The net requirements of Ca and P for an animal of 400 kg of BW were, respectively, 11.13 g and 5.40 g. To determine the total dietary requirements, endogenous losses and bioavailability values found in the literature were used to calculate the dietary requirements for maintenance which were added to the dietary requirements for growth to obtain the total requirements. The total dietary requirements of Ca, P, Mg, Na and K for an animal of 400 kg of BW, with average daily gain of 1,0 kg were, respectively, 34.59; 17.36; 7.82; 5.19 and 41.11 g/day. The macrominerals requirements of supplemented grazing Zebu cattle were similar o those recommended by the BR-Corte for Zebu cattle on feedlot.