The experimentwas conducted with the objective of predicting the dry matter (DM) digestibilityof rations for growing rabbits, by means of equations based on the concept ofideal nutritive entity. One hundred 42-day-old rabbits from the Botucatu GeneticGroup were used. Sixteen rations were tested, containing roughage (paper, corncobs, sugarcane bagasse or pine shavings), plus corn, soybean meal, soybeanoil, kaolin and common salt. Roughages were included at four levels, to obtain22, 28, 34 or 40% neutral detergent fiber (NDF) and 16% crude protein (CP).The experiment was accomplished in two periods, in a randomized block design.Positive linear effect of NDF on DM intake was observed. The means of DM digestibilityvaried between 60.10 and 80.78%. There was a negative linear effect of NDF,as well as of the NDF content × roughage interaction on the DM apparentdigestibility. Both CP and cell contents behaved as ideal nutritive entity,but the fibrous components did not. To predict DM digestibility, three modelswere tested; the best model was based on the cell contents, with true digestibilityfixed at 1; another on the NDF content, whose digestibility was predicted bymeans of an empiric equation; and the third one on the endogenous loss of cellcontents. The main difficulty in the formulation of models for apparent DM digestibilityprediction is to estimate, with precision, NDF digestibility and cell contentsendogenous loss. Future studies evaluating higher fiber levels in the dietsare needed. For diets with fiber content within the range tested in the presentstudy, model 3, which includes, besides neutral detergent fiber, acid detergentfiber and lignin, is recommended.
