The replacement of protein concentrates by synthetic lysine in the diet of growing pigs.

I . Pigs from 20 to 60 kg live weight were fed on cereal diets, supplemented only with vitamins and minerals, with and without supplementary lysine. 2. Growth rate, feed:gain ratio and carcass quality of pigs given a high-barley diet (75 barley meal, 23 % wheat offal) were inferior to those of pigs given a high-wheat offal diet (75 :h wheat offal, 23 yo barley meal). 3. On both diets, but particularly on the high-barley diet, performance was improved by the addition of L-lysine (to give a total lysine content of 5.2 g/16 g nitrogen, approximating to that present in a standard barley meal-wheat offal diet supplemented with 7 % white fish meal). 4. Percentage N retention was improved on both diets by supplementation with lysine. 5. Results for carcass composition showed that the carcasses of pigs fed on the unsupplemented high-wheat offal diet contained more lean tissue than those of pigs given the unsupplemented high-barley diet. Lysine supplementation resulted in an increased content of lean tissue on both diets, the percentage increase due to lysine being greater (but not significantly so) on the high-barley diet. The increased lean content was reflected in the carcass measurements but not in the total N retention values, which did not differ significantly between treatments. 6. The results are discussed in relation to the shortage and high cost of animal protein concentrates and the possible replacement of these concentrates with synthetic amino acids.