Availability of lysine in vegetable protein concentrates as determined by the slope-ratio assay with growing pigs and rats and by chemical techniques.

1. The availability of lysine in seven vegetable protein concentrates was determined using the slope-ratio assay with growing pigs and rats and with two chemical techniques. 2. With pigs, estimates of availability were lower using carcass compared to live-weight values, but there was no consistent effect of including food intake in the criterion of response. Availability estimates, using food conversion efficiency on a carcass basis were (proportion of total) linseed meal -0 . 23, lupin-seed meal 0 . 74, rapeseed meal no. 1 0 . 97, no. 2 0 . 77, sunflower meal no. 1 0 . 59, no. 2 0 . 66, no. 3 0 . 54. 3. Availability estimates for lysine with rats were also lower using carcass compared to live-weight values. Estimates based on food conversion efficiency were higher than those based on weight gain. Availability estimates in lupin-seed meal and sunflower meals were in general agreement with the pig estimates, whilst that with linseed meal was considerably higher (0 . 82). Assays were not conducted with rapeseed meal due to problems of food rejection with this meal. 4. The differences in available lysine were not detected by the chemical Silcock available-lysine test (Roach et al. 1967) nor by the direct fluoro-dinitrobenzene procedure (Carpenter, 1960).