Two experiments evaluated the partial replacement of soybean meal by encapsulated urea (Optigen®II, Alltech do Brasil, Curitiba, PR, Brasil). From a Control diet, 1kg of soybean meal was replaced by an isonitrogenous mixture containing 160g of Optigen®II + 2.5kg of corn silage in Exp.1, or 150g of Optigen®II + 850g of finely ground corn in Exp.2. In Exp.1, 61 Holstein cows were blocked and allocated to a treatment for 21 days, and measures of the same variable at the end of the standardization period were used as covariate. In Exp.2, 97 cows were allocated to a sequence of two treatments for 21 days, in a simple reversal (crossover) design. Response to treatments was evaluated from day 17 to 21. In both experiments, the nutrient composition of the offered diet and orts, orts as a % of the offered, body weight, and body condition score of the animals did not differ across treatments. Daily milk yield was 38.4kg/d for Control and 38.9 for Optigen®II in Exp.1 (P=0.62), and 27.0kg/d and 27.2 in Exp.2 (P=0.64), respectively. Encapsulated urea decreased milk fat content in Exp.2 (P=0.04). Optigen®II increased milk urea nitrogen from 16.3 to 17.3mg/dL in Exp.1 (P<0.01) and the ratios of milk produced to feed consumed (P=0.08) and allantoin to creatinine in urine (P=0.03) in Exp.2. Replacing soybean meal with Optigen®II did not induce lower performance.
encapsulated urea; non-protein nitrogen; Optigen