Balanço de nitrogênio e perdas endógenas em bovinos e bubalinos alimentados com níveis crescentes de concentrado

Abstract

The work objectived to evaluate the plasmatic and urine urea concentrations, the balance of nitrogen compounds, and to estimate the protein requirements for maintenance. It was used the equations recommended by the American and British systems, in four bovine and four bubaline steers, with initial average weight of 461,19±7,59 and 455.44±7,85 kg for the bovines and bubalines, respectively, distributed in two 4 x 4 Latin squares. The treatments consisted of different levels of concentrate (0.0; 24.0; 48.0; and 72.0%) composed by grinded corn, soybean meal, mineral salt, and Tifton-grass hay. Each period lasted 21 days, being 14 of adaptation and seven for collection. Samples of feces and urine (spot) were taken to estimate the production of fecal dry matter and urine volume. It was observed interactions between the species for N intake (NC), N-urine (UN) g/kg0,75 and urinary urea (UU); no interactions occurred for fecal-N (NF), absorbed-N (NABS), UN (g/d), balance of N (BN) and plasmatic urea (UP). Regardless of the difference observed between the species, the response variables increased linearly as the concentrate level increased. The increase of the concentrate level provided positive BN. The estimative of the metabolizable protein maintenance requirements of bovines and bubalines differs between the American and British systems.