NITROGEN-BALANCE IN GROWING PIGS AT VARIOUS ENERGY, THREONINE AND METHIONINE LEVELS

The nitrogen balance was assessed in the metabolic experiment with eig ht pigs of higher genotype (Seghers Hybrid) weighing 46 kg in average in four balance periods with two energy levels and two threonine and m ethionine levels using isoprotein and isolysine mixtures. In experimen tal 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 group s 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 m ixtures in groups I and III and higher in groups IP and IV. Higher ene rgy level and higher THR and MET levels affected positively the digest ibility and nitrogen retention, the significant difference was found o nly in crude protein retention per 1 kg of live weight and day (after the correction on mean crude protein ingestion) between groups I, II a nd 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 betw een 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). Significan t 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.