Availability of lysine in protein concentrates as determined by the slope-ratio assay with chicks and comparisons with rat, pig and chemical assays.

1. A slope-ratio assay was developed to determine the availability of lysine in protein concentrates for chicks, Two protein concentrates were assessed per assay, using three levels of incorporation into the basal diet. 2. Availability of lysine, expressed as a proportion of total lysine in five protein concentrates was: cottonseed meal 0.83, fish meal 1.00, meat-and-bone meal 0.86, soya-bean meal 0.93, sunflower meal 1.01. 3. The five protein concentrates had previously been assayed for available lysine with slope-ratio assays for pigs and rats (Batterham et al. 1979. Batterham et al, 1981). There was little relationship between the results for chicks and those for pigs and rats. For pigs, availability estimates ranged from 0.43 for cottonseed meal to 0.89 for fish meal. For rats, availability estimates ranged from 0.49 for sunflower meal to 1.04 for fish meal. 4. The results for chicks were in closer agreement with values obtained using the Silcock available-lysine assay (Roach et al. 1967) and the direct 1-fluoro- 2,4-dinitrobenzene procedure (Carpenter, 1060). By contrast, there was little relationship between the chemical tests and results for pigs or rats.