Comparison of high and low protein corn for growing-fattening pigs in drylot.

S INCE there is an enormous production of corn in the United States, a complete knowledge of its nutritive value is of scientific interest and may be of great economic importance. Yellow dent corn is too low in protein and its protein is too deficient in essential amino acids, especially lysine and tryptophane, to be fed most efficiently to growing pigs in drylot without a good protein supplement. Today, certain hybrid strains of corn contain up to 20%, or even more, of crude protein because of genetic selection and adequate nitrogen fertilization. In the production of high protein corn, the varieties containing above approximately twelve percent protein apparently have somewhat lower yields. Although whole corn protein is of low quality, the nutritional quality of corn germ protein is recognized as approximating that of animal proteins, both from feeding experiments and comparative amino acid analysis (Mitchell and Beadles, i944) (Block and Bolling, 1944). Zein, the alcohol-soluble protein of corn, constitutes the major protein of the endosperm and is extremely low in both lysine and tryptophane. Osborne and Mendel (I914) demonstrated that zein was nutritionally incomplete since rats lost weight on a diet containing zein as the only source of protein. Normal growth was restored by the addition of lysine and tryptophane to the diet. Their findings were further substantiated in feeding experiments by Hogan (i916) and Marias and Smuts (I94o), all of whom found that when zein or whole kernel corn was supplemented with lysine and tryptophane, normal growth occurred. As the protein content of corn is increased the zein fraction increases more proportionally than the non-zein fractions. As zein contains little, if any, tryptophane, it might be expected that corn with higher zein content would contain less tryptophane than corn with lower zein content. Actually there is a positive correlation between the protein content and tryptophane content since the non-zein protein fraction (containing tryptophane) also increases as the zein increases.