Efeitos nutricionais da substituição parcial do farelo de soja por uréia, em dieta de ovinos. Comparação da digestibilidade aparente e balanço de nitrogênio com a cinética do metabolismo da 15N-glicina

Six young (15 mo), castraded-male Corriedale sheep were fed diets where the soybean meal (D 1) was partially replaced by urea at two levels 0.7% (D2) and 1.4% (D3). All the diets were Rhodes-hay grass based, isoproteic (15.4% CP) and isocaloric (2.92 Mcal DE/kg). The animals were kept on each diet for 40 days according to a latin-square design (3x3). After a 21-day diet adaptation the animals were submitted to 7-day N balance (NB) and apparent digestibility coefficients (DC) studies and for a further 5-days for the whole-body protein metabolism study (WBP). The WBP was calculated by injecting (i.v.) hourly 15N-glycine (0.6 mg/kgBW/8h) and determining the urinary 15N-ammonium enrichment. The results showed similar dietetic intake, food conversion, body-weight (BW), weight gain (155-204 g/day), apparent crude protein digestibility coefficient (74-76%) and NB (6-7.3 g/day) for all diets. There were also no differences among treatments in 15N-flux, protein synthesis and breakdown values. According to the diets used in this experiment, and the results obtained, the comparison between the classical (BW gain, DC, NB) and simplified (WPD-NB) tests was possible.