111. The Nutritive Value of Proteins for Maintenance

Abstract

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.