OPTIMAL SUPPLY OF ALPHA-AMINO NITROGEN FOR GROWING PIGS .2. COMMUNICATION ON BALANCE STUDIES TO REDUCE N-EXCRETION

Based on 28 N balances carried out with 14 female pigs of 50 kg live weight it was investigated to which extent the dietary protein supply can be reduced in order to combine maximum N retention with minimum N excretion. At constant supply with all essential amino acids (10.5 g lysine/kg) the crude protein content of the diet was reduced in 7 steps from 170 g to 100 g/kg (13,5 MJ ME). The proportion of each essential amino acid to lysine was held constant in each step by supplementation of amino acids in pure form. Daily protein supply could be reduced up to 2 g N/kg LW0.75 in order to combine maximum N retention (1.23 g N/kg LW0.75) with minimum N excretion. Further reduction of protein supply diminished beside N excretion also N retention indicating a deficiency of non-essential amino acids. At the minimum protein supply N utilisation was improved from 53 % to 60 % and biological value from 74 % up to a maximum of 93 %. Plasma urea correlated significantly with N excretion. The deficiency of alpha-amino N increased linearly most of the essential amino acids of the blood plasma. Based on regressions a minimum supply of crude protein of 12.6 g/kg LW0.75 was derived, with a proportion of essential (without arginine):non-essential amino acids of 47:53. The lysine content within the protein should amount to 7.3 %. To utilize the protein retention capacity a minimum protein content of 14% per 13 MJ ME/kg was calculated.