BALANCE STUDIES WITH GROWING PIGS TO REDUCE N-EXCRETION .1. OPTIMAL SUPPLY WITH ESSENTIAL AMINO-ACIDS

Based on 28 N balances carried out with 14 female pigs of 50 kg live weight it was investigated which amounts of essential amino acids whose profile corresponded to an ideal protein a pig has to ingest in order to combine maximum N retention with minimum N excretion. At constant crude protein level of 150 g/kg of a peas-barley-diet the proportion of essential amino acids was gradually increased in 7 steps, starting from 5% lysine up to 8% lysine in the protein. The proportion of each essential amino acid to lysine was held constant in each step and was adjusted by supplementation of amino acids in pure form. Daily N retention increased at the 5% lysine level linearly from 0.9 g N/kg LW0.75 to the maximum of 1.24 g N/kg LW0.75 at the 7% lysine level. Maximum N retention corresponded to a daily intake of lysine an essential amino acids of 0.91 g and 5.94 g/kg LW0.75, respectively. A higher amino acid supply had no further effects on N balance. At this optimal supply total N excretion declined by 30%. Thereby N utilisation was improved from 42.4% up to a maximum of 61.8% and biological value increased from 65% to 85%. Concentrations of urea and free amino acids in blood plasma supported the above mentioned supply level. As practical recommendation for reduction N excretion of growing pigs of 50 kg live weight a lysine: energy proportion of 0.76 g/MJ ME and a proportion of essential (without arginine): - non-essential amino acids of 45:55 was derived.