Raçoes com diferentes teores de proteína degradada no rúmen, para vacas em lactaçao. 2. Taxa de passagem, digestibilidade e energia líquida da silagem de milho

This work was carried out with the objective to evaluate the effects of four concentrate diets with different contents of rumen degraded protein (RDP) on the ruminal and intestinal digesta passage rate, apparent digestibility and the not energy value of corn silage. Twelve lactaing cows 60 days post-calving were fed with ad libitum corn silage (Zea mays L.) and 1 kg of concentrate diets for each 2.5kg of milk produced, on a completely randomized design. The percentage composition of diets were: R I - ground corn grain (GCG - 50.5), ground soybean grain (GSBG - 40.0) and cottonseed meal (CSM - 6.8); R2 - GCG (69.2). CSM (26.7) and urea (U - 1); R3 GCG (42.6), CSM (53.9) and U (1) and R4 GCG (38.3), CSM (54.7), bone and meat meal (3.0) and fish meal (3). Mineral supplement and antioxidant were added to all diets. The apparent digestibility coeficients of nutrients were not affected by treatments. Higher digesta passage rate was found when the cows were fed R2 diet, and showing a lower digesta retention time in the rumen and in the intestinal tract, as a whole. The R3 diet showed higher digesta retention time in the rumen and lower retention in the intestines. The highest pos-ruminal digesta passage rate (R2) was found for R4 diet. The average net energy value of corn silage was 1.01 Meal / kg dry matter, that resulted in lower protein utilization and lower digestibilities coeficients. (RA)