An evaluation of total lysine as a predictor of lysine status in protein concentrates for growing pigs.

1. Eight protein concentrates were compared on a total lysine basis in lysine-deficient diets for pigs during the 20--45 kg growth phase. Each diet was also supplemented with free lysine to verify that lysine was the first limiting amino acid. 2. With fish meal, skim-milk powder, rapeseed meal and soya-bean meal growth rates and feed conversion efficiencies were similar and superior (P less than 0.05) to those produced with cottonseed meal, two meat meals and sunflower meal. 3. The response to added free lysine confirmed that lysine was the first limiting amino acid in all diets except skim milk, where the growth response was not significant (P less than 0.05). 4. The growth response of the pigs indicated that the availability of lysine in cottonseed meal, the two meat meals and sunflower meal was reduced by approximately 60% compared to that in the other protein concentrates. 5. Rat bio-assay estimates of the availability of lysine in the protein concentrates were in general agreement with those calculated from the response in pigs. There was little relationship between the Silcock estimates for lysine availability for the cottonseed, meat meals or sunflower meal relative to either the rat bio-assay estimates or the response of pigs.