The experiment was conducted with the objective of predicting the dry matter (DM) digestibility of rations for growing rabbits, by means of equations based on the concept of ideal nutritive entity. One hundred 42-day-old rabbits from the Botucatu Genetic Group were used. Sixteen rations were tested, containing roughage (paper, corn cobs, sugarcane bagasse or pine shavings), plus corn, soybean meal, soybean oil, kaolin and common salt. Roughages were included at four levels, to obtain 22, 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 digestibility varied 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 apparent digestibility. Both CP and cell contents behaved as ideal nutritive entity, but the fibrous components did not. To predict DM digestibility, three models were tested; the best model was based on the cell contents, with true digestibility fixed at 1; another on the NDF content, whose digestibility was predicted by means of an empiric equation; and the third one on the endogenous loss of cell contents. The main difficulty in the formulation of models for apparent DM digestibility prediction is to estimate, with precision, NDF digestibility and cell contents endogenous loss. Future studies evaluating higher fiber levels in the diets are needed. For diets with fiber content within the range tested in the present study, model 3, which includes, besides neutral detergent fiber, acid detergent fiber and lignin, is recommended.
acid detergent fiber; cell content; crude protein; equations; neutral detergent fiber; nutrition
