Balanço de nitrogênio em suínos, machos castrados (15-30 kg), alimentados com baixa proteína e diferentes níveis de isoleucina digestível

Twenty crossbred castrated barrows, averaging 22.26 ± 1.79 kg of body weight, were used. The animals were individually alloted in metabolic cages, in a randomized blocks design, with five treatments (0.45, 0.52, 0.59, 0.66 and 0.73 % of digestible isoleucine) and four replicates. The diets were based on corn and soybean meal with low crude protein (14.15 %) and different levels of digestible isoleucine. The diets were humidified and supplied twice a day (7 am and 7 pm) to reduce losses and facilitate ingestion. The experimental period lasted 12 days, being 7 days for adaptation to metabolic cages and experimental diets and 5 days for total feces and urine collection. Feces were analyzed for dry matter and nitrogen (N), whereas urine samples were analyzed for N. The plasma urea nitrogen was also determined. Then, the N intake, N excretion (feces and urine), N absorbed, N retention, N retention/N intake, N retention/N absorbed and total N excretion were determined. Only N intake (g/kg BW0.75/day) was influenced (p<0.05) by digestible isoleucine levels, showing a linear increase on N intake as digestible isoleucine levels increased in the diets.