Estimation of the undegradable fraction of neutral detergent fiber of the tropical forages from lignin concentration

Abstract

The potential undegradable fraction of neutral detergent fiber of tropical grasses predicted through the equations adopted by the nutritional systems CNCPS and NRC-2001, were validated. The equation recommended by NRC-2001 was used with (NRCII) or without the empiric correction factor proposed of Detmann et al. (2004). A total of 540 samples were used, obtained from manual grazing simulation and esophageal extrusa, from hays and from tropical grasses submitted to different fertilizing levels and cutting ages, cultivated in Campos dos Goytacazes-RJ, Brazil. The samples were analyzed for dry mater, lignin in sulfuric acid (LAS), lignin in potassium permanganate (LPER), undegradable fraction of neutral detergent fiber (FDNi), the last one was done by rumen in situ incubation of the samples for 240 hours. The data were analyzed by the Pearson’s linear correlation method, while, the comparative evaluation regarding the prediction efficiency among the nutritional models was done through the evaluation and partition of the mean square errors. Among the examined nutritional models, it shown that corrected NRC-2001 presented better results in the simulation, independent of using LAS or LPER. This suggest the fact that gravimetric estimates of lignin levels present in the feed don't allow to predict potentially with accuracy the dimension of the fraction digestible or indigestible of the neutral detergent fiber.