The Nutritive Value of Proteins for Maintenance

The results of the present experiments may be summarised as follows: (1) When minimal quantities of protein are fed in the maintenance rationof steers, a deficiency of lysine will lead to a marked increase in the urinary N output. A deficiency of cystine has no effect. (2) The catabolism of body tissue is shown by the high creatine excretionand the S: N ratio of the excess S and N excreted. This is probably the resultof excessive deamination with the production of a mild acidosis. (3) As regards urinary partition of N there is some indication that alysine-deficient diet causes a decreased percentage excretion of urea N and anincrease of ammonia N. (4) The biological values have been calculated, the only marked difference occurring with wheat gluten, a protein very deficient in lysine (5) An approximate value for the lysine requirements for maintenance has been calculated, i.e . 0·80 g. lysine N per 1000 lb. live weight.