Nitrogen balance in growing pigs at various energy, threonine and methionine levels

The nitrogen balance was assessed in the metabolic experiment with eight pigs of higher genotype (Seghers Hybrid) weighing 46 kg in average in four balance periods with two energy levels and two threonine and methionine levels using isoprotein and isolysine mixtures. In experimental groups I to IV, the average ingestion of crude protein was 257.9 g and LYS 14.7 g per pig and day. In feeding mixtures for pigs in groups I-II and III-IV the content of ME amounted to 12.9 and 13.6 MJ in 1 kg of mixture, respectively. The levels of THR and MET were lower in mixtures in groups I and III and higher in groups IP and IV. Higher energy level and higher THR and MET levels affected positively the digestibility and nitrogen retention, the significant difference was found only in crude protein retention per 1 kg of live weight and day (after the correction on mean crude protein ingestion) between groups I, II and IV (2.50; 2.80 and 3.11 g; P < 0.01) and between groups I and III, and/or III and IV (2.50 and 2.82 g, and/or 2.82 and 3.11 g; P < 0.05). Significant differences were also found in the fat digestibility between groups I, II and III, IV (P < 0.01), and/or between groups III and IV (P < 0.05) and in ash digestibility between groups I, II and III, IV (P < 0.01), and/or between groups III and IV (P < 0.05). Significant differences were found in THR digestibility between groups I and II, III and IV (P < 0.01), and/or between groups I and III (P < 0.05) and in MET digestibility between groups I and II, III and IV (P < 0.01). The above mentioned differences were connected with the application of soya oil in groups III and IV and synthetic THR and MET in groups II and IV.