This experiment was conducted to evaluate the levels of total threonine in diets for gilts from 30 to 60 kg of live weight. Forty females, with initial average weight of 29.2 ± 1.4 kg, were used in an experimental design of randomized blocks, with five treatments (0.60; 0.65; 0.70; 0.75 and 0.80% of total threonine), four replications and two animals per experimental unit. The basal diet with 18% of crude protein and 0.928% of total lysine, attended the requirements of gilts according to NRC (1988), except for threonine. The basal diet was supplemented with L-threonine resulting in experimental diets that supplied a calculated digestible threonine:digestible lysine ratio of 62, 68, 74, 80 and 86%, respectively. The experimental diets and water were supplied to gilts ad libtum. At the final of experimental period, when gilts reached the average weight of 59.98 ± 2.9 kg, were collected blood sample to determinate the level of urea in blood serum and one animal per experimental unit was slaughtered to evaluate the protein deposition rate. It was observed effect of threonine levels on weight gain of animals, that linearly increased. Feed intake quadratically increased up to 0.66% of threonine in diet. The treatments influenced the feed:gain ratio that reduced until level of 0.70%. The calculated ratio of true digestible threonine:true digestible lysine at level that proposed the best values of feed:gain ratio, corresponded to 75%. It was not observed effect of treatments on level of urea in blood serum. The dietary levels of threonine also influenced the protein deposition rate, that quadractly increased of way until the level of 0.70%. It was concluded that gilts with high genetic potential, from 30 to 60 kg live weight require 0.70% of total threonine and a calculated ratio of true digestible threonine:lysine of 75%.
gilts; growing phase; requirements; threonine
