The effect of theprotein and (or) carbohydrates supplementation on the rumen degradation of neutraldetergent fiber (NDF) from low quality forage was evaluated. The experimentsimulated the supplementation of finishing cattle grazing low quality Brachiariadecumbens pasture during dry season (70:30 forage to concentrate ration,%DM). The concentrate referring to the basal treatment was formulated to contain30% CP, using starch as the energetic source and casein as the protein source.The treatments were established by omission of protein and (or) carbohydratessources, associated with substitution of starch by pectin. In that way, sixtreatments were evaluated: 1. Forage, 2. Forage plus Starch, 3. Forage plusPectin, 4.Forage plus Casein, 5. Forage plus casein plus starch and 6. Forageplus casein plus pectin. The treatments were evaluated under rumen environment,simulated by in vitro incubation, where the experimental diets were submittedto different incubation periods: 0, 3, 6, 9, 12, 24, 36, 48, 72, and 96 hours.The incubation procedure was repeated four times in a way that four evaluationswithin each incubation time were done for each treatment. The incubation residueswere evaluated according to its contents of NDF and interpreted using a non-linearlogistic model. It was observed that the degradation rate of potentially degradableNDF (pdNDF) was increased almost 46% with casein supplementation, resultingin an increment of 14.6% on the effective degraded fraction. A minor effectwas observed with the inclusion or substitution of the supplemental carbohydratesource. The starch supplementation resulted in reduction on pdNDF degradationrate, whereas the supplementation with pectin did not affected this parameter,when compared to no carbohydrate supplementation. In the presence of casein,the starch supplementation raised the discrete lag time for NDF degradation.
