REDUCING CRUDE PROTEIN-CONTENT WITH SUPPLEMENTATION OF SYNTHETIC LYSINE AND THREONINE IN BARLEY - RAPESEED MEAL - PEA DIETS FOR GROWING PIGS

This study was conducted to determine the possibility to use synthetic amino acids to lower the nitrogen output from pig production. A perfo rmance experiment was carried out with 120 triplet-fed growing pigs wh ose dietary crude protein was reduced from 179 g/feed unit (FU = 0.7 k g starch equivalent) to 160, 140 and 122 g/FU, respectively. The diets were supplemented with synthetic lysine and threonine to keep the lev el of these amino acids constant. Dietary protein reduction did not af fect the growth performance or feed conversion ratio of the pigs, but it did linearly increase the portion of fat to lean in the carcass. Si gnificant linear effect was found in back fat (p < 0.001) and side fat thickness (p < 0.01) and in the proportion of lean in valuable cuts a nd in whole carcass (p < 0.05). However, the change in carcass composi tion was negligible down to a crude protein level of 140 g/FU. It may, therefore, be concluded that the crude protein content of the diet ca n be reduced by up to 20% by balancing the dietary protein with synthe tic lysine and threonine.