The objective of this work was to evaluate the effect of association of forage cactus to sugar cane bagasse and urea on nitrogenous compounds balance and microbial protein synthesis in milk heifers supplemented or not. Twenty-five Holstein-Gir crossbred heifers with average of 227 kg of LW were used, kept in feedlot system and assigned to a randomized block design, established in accordance with the weight of animals. The control ration was composed of 64.0% of forage cactus, 30.0% of sugar cane bagasse, 4.0% of urea:ammonium sulphate mixture (9:1) and 2.0% of mineral mixture, in DM basis. The heifers were supplemented based on the live weight (0.5% of the LW). The supplements had characterized the treatments, together with the control treatment. The tested supplements were: wheat meal, soybean meal, cottonseed meal or whole cottonseed. The proportion of ingredients in experimental rations for supplemented animals was: 57.0% of forage cactus, 26.0% of sugar cane bagasse, 3.5% of urea:ammonium sulphate mixture, 1.8% of mineral mixture and 11.7% of supplement. The nitrogen balance was not influenced by treatments, presenting average value of 49.3 g/day. The cottonseed meal or soybean meal supplementation increased the nitrogen urinary excretion, the urea concentration and urea nitrogen in the serum and the urea urinary excretion and urea nitrogen. The association of forage cactus to sugar cane bagasse and urea, without the use of supplements allowed microbial synthesis efficiency of 105.0 gCPmic/kg of consumed TDN. The whole cottonseed supplementation provided greater alantoin and purine derivatives urinary excretion and better microbial synthesis efficiency, being, therefore, the most indicated in such conditions.
fiber; microbial synthesis; nonprotein nitrogen; Opuntia fícus; supplementation
