The objective was to evaluate the effect of the substitution of corn silage by coffee husk in diets for dairy heifers on the ruminal variables, nitrogenous compounds and e microbial protein production. Twenty-four dairy Holstein heifers, purebred and crossbred, were assigned to a randomized block design, with four treatments and six blocks, according to the animal initial weight. The treatments were four coffee hulls levels: 0.0, 7.0, 14.0, and 21.0 (% DM total), in substitution of corn silage. Daily, all the heifers was fed with 2 kg of concentrate The nitrogenous (N) compounds intake and and fecal N excretion linearly ncreased with the substitution of corn silage by coffee husk that resulted in positive N balance, with average of 22.31 g/day for all the diets, however, the percentage of N absorbed in relation to the consumed reduced linearly. The ruminal ammonia concentrations and the plasma urea concentration (NUS), average of 11.93 and 10.08 mg/dL respectively, was not affected by the inclusion of coffee husk in the diet. The excreções of acid úrico, alantoína and purina derivatives, the absorbed purinas, the microbial N (N mic) and the microbial efficiency (Efic M) linearly reduced with the partial substitution of corn silage coffee husk. Observing reduction of 1,08 g/day of Nmic and 1.96 gPB/kg NDT of Efic M per unit of coffee husk added to the diet. The inclusion of coffee husk in levels of up to 21% DM in diets for dairy heifers reduces the microbial nitrogen production and the microbial efficiency, what could be harm to the animal performance.
ammonia; microbial efficiency; nitrogen; plasma urea; purine derivatives
