Valor energético de dietas para bovinos obtido por respirometria calorimétrica

We used data from experiments with Zebu cattle and their crosses in the Calorimetry Labora-tory and Metabolism Animal of Veterinary School of UFMG between 2009 and 2015 to assess the energy value of tropical diets and develop equations for predicting methane production. They were used data of the total collection the faeces stool for five consecutive days and the estimates used by the NRC (2001) model to evaluate relations of the energy value, expressed in different ways. Methane production was determined in respirometric chamber by the tech-nique of calorimetry indirect. There were obtained two equations with a single variable each, DMI (kg/day) and IGE (MJ/day). The animals were in growing, termination, pregnancy and lactation, had live weight of 180-683 kg and were fed in the nutritional plans of maintenance, ad libitum and intermediate (mild gains 0.5 to 0.6 kg/day ) with forage-based diets or forage-based and concentrated. The concentrates were composed of corn milled, soybean meal and mineral supplement. The forages used included Tifton-85 (Cynodon spp) hay and sorghum si-lage (Sorghum bicolor), corn (Zea mays) and Tanzania grass (Panicum maximum cv. Tanzania). The model proposed by the NRC (2001) underestimated the values of TDN (P<0.01), of EE (P<0.01) digestible, of NFC (P <0.01) digestible, and of NDF digestible (P<0, 01). The rela-tionship between the concentration of digestible energy and TDN percentage was 0.0348. The relationship between metabolizable energy and digestible energy was greater than 0.82. Esti-mates of the NDT through the model proposed by the NRC (2001) not corresponded the esti-mates obtained in vivo in tropical condition. The main determinant of the daily production of methane was the intake of dry matter, expressed in kg/day (QMR = 0.61 and CP = 27.2).

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