Desempenho nutricional de bovinos em pastejo suplementados durante os períodos de transição seca-águas e de águas

• Autor(a) principal: Figueiras, Janderson Florencio
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1858
• topic: Suplementação; Pastos tropicais; Consumo; Supplementation; Tropical pastures; Consumption; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA

This Thesis was based on two experiments with beef cattle under grazing in signal grass pastures (Brachiaria decumbens Stapf) pastures. The first experiment was carried out during the dry-rainy transition season and aimed to evaluate the effects of different amounts of a protein supplement on intake, digestibility, transit and degradation dynamics of fibre, and metabolic characteristics of nitrogen utilization. Five Nellore bulls fitted with rumen cannulated, averaging 273 kg of body weight (BW), were used. The animals grazed five signal grass paddocks (0.34 ha) and had access to water and mineral mixture all time. The experiment was carried out according to a 5 × 5 Latin square design, with five treatments and five experimental periods. The treatments consisted of five different amounts of offered supplement: 0, 1.25, 2.5, 5.0, and 10.0 g/kg BW. The supplementation was composed by soybean meal (588.8g/kg as fed), corn (382.3 g/kg as fed), urea (26.0 g/kg as fed) and ammonium sulphate (2.9 g/kg as fed) in order to present 340 g of crude protein (CP) per kg (as fed). The dry matter (DM), organic matter (OM), CP, and digested OM intakes increased linearly (P<0.10) as the amount of supplement increased. with increment of supplementation. Despite this, there was no effect of supplement amounts (P>0.10) on pasture and neutral detergent fibre (NDF) intakes. The total and ruminal digestibility of OM and CP were linearly increased (P<0.10) as supplement amount increased. Despite this, no effect was verified (P>0.10) upon digestibility of NDF. The rumen ammonia nitrogen (RAN) concentration increased linearly (P<0.01) according to amounts of supplement. The increase in the supplement amount increased linearly (P<0.01) the nitrogen balance in the rumen and animal body, and the production of microbial nitrogen in the rumen (NMIC). There were no effect (P>0.10) neither on transit nor degradation of fibre in the rumen. It has been concluded that protein supplementation for grazing cattle during dry-to-rainy transition season does not affect pasture intake. Despite this, the supplementation increases the nitrogen balance and the efficiency of nitrogen utilization. This seems to be caused by an improvement on the nitrogen status in the animal metabolism. The xobjective of the second experiment was to evaluate the effects of different protein concentration in the supplement on intake, digestibility, transit and degradation dynamics of fibre, and metabolic characteristics of nitrogen utilization in cattle under grazing during rainy season. Five crossbreed Holstein × Zebu bulls, fitted with rumen and abomasum cannulas, averaging 296 kg BW, were used. The animals grazed five signal grass paddocks (0.34 ha) and had access to water and mineral mixture all time. The experiment was carried out according to a 5 × 5 Latin square design, with five treatments and five experimental periods. The treatments were: control (without supplementation), and supplements containing 0, 330, 670 and 1000 g CP/kg as fed. All supp1ements were provided to the animals at 1 g/kg BW. Corn starch was used as the supplement containing 0 g CP/kg. The supplement containing 1000 g CP/kg was composed by soybean meal, urea, and ammonium sulphate. The other supplements were produced by replacing the protein supplement for starch. The intakes of DM, pasture, OM, CP and digested OM were increased (P<0.10) by supplementation. Moreover, there was a positive and linear effect (P<0.10) of CP content in the supplement on DM, pasture, OM, CP and digested OM intake. Despite this, the supplementation did not affect (P>0.10) the total and ruminal digestibility of OM and CP but increased (P<0.10) the total digestibility of NDF. The increase of CP content in the supplement caused a positive and linear effect (P<0.10) on total and ruminal digestibility of OM and CP and also a quadratic effect (P<0.10) on total digestibility of NDF and diet content of digestible OM. The RAN concentration was increased (P<0.10) by supplementation and also presented a linear and positive relationship (P<0.10) with the CP content in the supplement. There were no effect (P>0.10) neither on transit nor degradation of fibre in the rumen. On average, the nitrogen balance in the animal body was not affect by supplementation (P>0.10). Despite this, the nitrogen balance were linearly increased (P<0.10) as the CP content in the supplement increased. The NMIC was increased (P<0.10) by supplementation and also presented a linear and positive relationship (P<0.10) with the CP content in the supplement. It has been concluded that protein supplementation for grazing cattle during rainy season can increase the voluntary intake of pasture and also improve the efficiency of nitrogen utilization when compared to energy supplementation. This seems to be caused by an adequacy of overall metabolism and an improvement on the nitrogen status in the animal metabolism.