Níveis de Proteína Bruta para Leitoas dos 30 aos 60 kg Mantidas em Ambiente de Conforto Térmico (21oC)

this experiment was conducted to evaluate levels of crude protein (cp) for gilts in growing phase, maintained under thermal comfort. the internal temperature at room was kept during the experimental period in 21.3 ± 0.53°c with relative humidity of 70.5 ± 5.11%. the calculated black globe humidity index (bghi) in this period was 68.7 ± 0.93. forty crossbred gilts with average initial weight of 29.4 ± 1.42 kg were used in an experimental design of randomized blocks with five treatments (16, 17, 18, 19 e 20% de cp), four replicates and two animals per experimental unit. the experimental isoenergetics rations with 3,400 kcal of de/kg, were formulated to meet the requirements of animals, except to cp. the rations and water were feeding ad libitum to animals, until the final of experimental period when gilts reached the average weight of 60.6 ± 1.76 kg. the cp level of ration influenced the average daily weight gain (adwg) that increases and the feed:gain (f:g) ratio that improved linearly. in spite of linear effect of cp levels on adwg and f:g ratio the model of "linear response plateau" (lrp) was one that better adjusted to the data estimating respectively in 18.78 and 19.15% the levels of cp occurred a plateau. the daily intakes of protein and lysine increase linearly with crescent level of cp on ration. however it did not observe effect of cp levels on daily intakes of ration and digestible energy. it was concluded that gilts from 30 to 60 kg kept under thermoneutral environment require 19.15% of cp on ration associated with the intakes of 343 e 19.08 g/day of crude protein and lysine, respectively for better performance.