This study was conducted to evaluate levels of digestible lysine for pigs at 30 to 60 kg kept under heat stress. It was used 70 castrated animals kept in environment at 30ºC and others 70 kept at 34ºC, distributed in a randomized block design, with five treatments (0.83, 0.93, 1.03, 1.13 and 1.23% digestible lysine), and seven repetitions with two animals per experimental unit. The daily weight gain of the animals kept at 30ºC increased up to 1.04% of digestible lysine, whereas it did not change at 34ºC. Feed daily intake of animals at 30ºC and 34ºC did not change with levels of lysine. Daily lysine intake of animals, in both environments, increased according to the level of lysine in the diet. At 30ºC, feed conversion improved up to the level of 1.07% lysine, whereas at 34ºC, it did not vary among lysine levels. Regardless of the temperature, use efficiency of lysine decreased as levels of lysine increased and it was 4.4% worse in the environment with higher temperature. Protein deposition in carcass in the 30ºC environment increased up to the level of 1.05% lysine, but it did not change at 34ºC. At 30ºC, fat deposition decreased down to 1.08% lysine, whereas in the 34ºC environment, it increased up to 1.08%, and it was on average 25.6% lower than at 30ºC. Levels of triiodothyronine and thyroxine were 35 and 30%, respectively, which was lower in animals kept in the 34ºC environment, where respiratory rate and rectal temperature were higher than those observed in animals kept in the environment at 30ºC. The levels of 1.04 and 0.83% of digestible lysine provide greater weight gain and protein deposition in pigs kept in environments at 30ºC and 34ºC, respectively.
amino acid; environment; performance; temperature; thyroidal hormones
