Nutrient intake and digestibility and ruminal parameters in beef cattle fed diets containing Brachiaria brizantha silage and concentrate at different ratios

Nutrient intake, total apparent and partial digestibility, ruminal pH and ammonia (NH₃-N) concentrations were evaluated in beef cattle fed diets containing Brachiaria brizantha cv. Marandu silage and concentrate levels of 200, 350, 500 and 650g/kg dry matter base. Four crossbred Holstein x Zebu rumen and abomasum fistulated steers, 224±23kg-average initial live weight, were assigned to a 4x4 Latin square design. Chromic oxide was used as marker for estimates of faecal and abomasal dry matter flow. dry matter (DM), crude protein (CP), ether extract (EE), total carbohydrates (TCHO) and non-fibrous carbohydrates (NFC) (kg/d) intakes increased linearly (P<0.01) with concentrate increase in the diets but aNDF (neutral detergent fiber) intake (kg/d) decreased linearly (P<0.01). The DM and organic matter (OM) total apparent digestibilities were influenced (P<0.05) quadratically by the concentrate levels in the diets, estimating maximum values of concentrate levels of 504 and 507g/kg DM, respectively. Total digestibilities of other nutrients were not influenced (P>0.05) by the diets. Concentrate level only affected apparent ruminal and intestinal digestibility for DM, CP and EE, using an adjusted quadratic equation (P<0.05) for DM and a linear equation for the others. Average pH values were normal in all the treatments for ruminal fermentation. The diets with concentrate levels of 200, 350, 500 and 650g/kg DM presented a maximum NH₃-N concentration of 25.4; 26.7; 20.8 and 29.0mg NH₃-N/dL, respectively, at 3.26; 2.64; 2.19 and 2.52h. Diets containing concentrate levels of 200 and 350g/kg DM, supplemented with B. brizantha silage, resulted in low nutrient intake, which can lower animal performance. However, the ruminal fermentation pattern was not influenced by the diets. Thus, the B. brizantha silage may be a good alternative as forage source in beef cattle diets. However, its use depends on good alimentary planning with an appropriate integration between pasture management and forage surplus conservation in the form of silage.