Avaliação nutricional das tortas de algodão e girassol por meio da técnica in vitro de produção de gases

Abstract

The objective of this study was to evaluate the effect of levels of cottonseed cake (CC) and sunflower cake (SC) (0, 7, 14, 21 and 28 % dry matter basis - DM) in the feedlot wethers diets on the kinetic parameters of in vitro gas production, and to use these parameters to predict total DM digestibility of the diet and compare these estimative with the values observed in animals by simulation. In vitro incubations were carried out simultaneously to in vivo experiments in which were tested diets (forage:concentrate ratio of 40:60) containing CC and SC levels by a 5 x 5 Latin square design. Five rumen fitted sheep were used in the in vivo trials, from of which the ruminal fluid was collected for in vitro incubations, and where were collected the data of organic matter digestion (OM). In vitro incubations were used to evaluate the effects of diet, animal and experimental period, have been incubated the same diets and ingredients used on in vivo trials. Kinetic parameters obtained by in vitro gas production technique (IVGPT) as well as chemical composition of diets have been used to estimate the organic matter digestion for all experimental diets. The increase in CSC levels in the diets caused a reduction on total gas production (GT) for evaluated foods, and reduction on gas production from rapidly degradation fraction (Vf1) for soybean meal (SBM), CSC and corn silage (CS), and gas production from slowly degradation fraction (Vf2) for SBM and CS. The CSC levels had a cubic effect on digestion rates (c1 and c2), except c1 to SBM. The increase in SC levels in the diet caused a reduction on GT production for ground corn (GC), SC and CS. A decrease on gas form Vf1 for SBM and CS, and Vf2 for SBM and SC have been observed. The SC levels had linear and quadratic effects on digestion rates (c1), respectively, for SBM and CS, linear effect on c2 for SBM and cubic effect for SC and CS. It was observed animal effect on Vf1, Vf2, and GT, as well as a period effect on latency (L) and Vf2. The diet of the donor animal, the animal and the trial period for both CSC and for SC affect kinetic parameters of in vitro gas production and thus should be considered in these kinds of trials. The simulation of the predicted and observed values for the digestion of OM showed similarity for CSC levels, but the same behavior was not observed for SC levels. But when we have used the data together there was no differences between predicted and observed values. Thus, IVGPT can be used to assess the overall digestion diets, due to its high sensitivity to the variation of composition of the diets.