The Comparative Nutritive Value of Corn of High and Low Protein Content for Growth in the Rat and Chick

Abstract

A series of corn samples, ranging in protein content from 6.8% to 13.6%, was employed in feeding experiments with rats and chicks. The low-protein varieties (range of 6.8 to 9.1% protein) were markedly increased in their protein content (9.5 to 13.6% protein) by increased rates of nitrogen fertilization. The high-protein samples were superior to the low-protein samples when fed on the basis of equal proportions of corn grain in the diet. The low-protein corn was found to be deficient in at least the following amino acids: lysine, tryptophan, isoleucine, threonine and valine. In contrast, the high-protein corn was deficient in only lysine and tryptophan, although not as severely deficient as the low-protein corn. However, when the corn was fed on the basis of equal protein content in the diet, the high-protein corn was somewhat inferior to the low-protein corn, reflecting a greater proportion of zein in the protein. Studies on the supplementation of corn diets with various natural protein materials indicated that soybean meal is the most satisfactory of those tested. The protein supplements were most effective when added to the high-protein corn diets.