An experiment was conducted to study the effects of allowance of ammoniated rice straw on the voluntary intake (VI) and digestibility of dry matter (DMD), and on the intake, excretion, digestibility and N balance. Fifteen adult sheep, males, castrated, with average weight of 63.8 kg, individually kept in metabolic cages, were used. The levels of straw fed to the animals were: 1.5; 3.0; 4.5; 6.0 and 7.5% of live weight. A supplement (200 g/animal/day of corn) was used to supply available energy to the ruminal microorganisms. There was no effect of the level of straw offer on DMD, excretion of N in the urine, digestibility and balance of the N, and the average values were 58.6%, 8.23 g/day, 44.7% and 0.29 g/day, respectively. There was linear effect of the offer level on the intake and excretion of N in the feces. The DM and DMDs intake linearly increased up to 3.0 and 4.3%, respectively. These allowance levels produced 23.9 and 37.4% of orts, respectively. Based on the intake of DMD above the maintenance requirements (0.12 digestible energy Mcal/kgPV0.75), to maximize the animal performance per unit of straw fed is recommended to supply about 123.05 g/kgPV0.75 of ammoniated rice straw. When the objective is just to meet the maintenance requirement of the animals, levels lower than 123.05 g/kgPV0.75 are accepted. Higher levels are not recommended, therefore there would be waste of straws without increment in the animal response.
allowance levels; ammonization; digestibility; nitrogen balance; urea; voluntary intake
