An experiment was conducted at the Department of Animal Husbandry of Universidade Federal de Lavras aiming to study the nitrogen and energy balance in diets with reduced crude protein rates (CP) and different levels of energy and lysine for growing pigs. 52 castrated pigs (initial weight = 36.13 ± 2.8 kg) of high genetic potential were used, housed individually in metabolism cages (experimental unit). The treatments consisted of 12 diets with three levels of metabolizable energy (ME) (3060, 3230 and 3400 kcal / kg) and four of true digestible lysine (TDL) (0.7, 0.9, 1.1 and 1, 3%) with 14% CP plus a control diet with 3230 kcal ME / kg, 1.03% TDL and 18% CP. We used a DBC in time 3x4 +1 factorial design with four replications to verify the absorbed nitrogen (AN), N retained (NR), the NR / NA (%),absorbed energy (AE), retained energy (RE) and the ratio RE /AE (%). In relation retained nitrogen / absorbed nitrogen was declining linear regression (P <0.05) when 3400 kcal / kg was used, where the lowest levels (0.7 and 0.9%) of TDL showed the best results. In the study of energy balance, for the variables retained energy and the relationship between energy there was no difference (P> 0.05) between the control treatment and other experimental diets. It is concluded that the levels 3230 kcal / kg and 1.03% of TDL can be used without affecting the utilization of nitrogen by growing pigs in diets with reduced crude protein content.
Synthetic amino acids; nutrition; metabolism; ideal protein
