Peer review

Four experiments were conducted to compare the protein quality and amino acid balance of a number of opaque-2 corn varieties and a floury-2 corn with normal hybrid corn for the growing pig. Pigs fed opaque-2 corn produced the faster gains of the three corn types on either an equal weight substitution or an isonitrogenous basis. On an isonitrogenous basis, floury-2 corn and normal corn diets resulted in similar gains. The particular variety of floury-2 corn tested was concluded to have a protein quality very similar to that of normal corn for the growing pig. Pigs fed normal corn supplemented with the six most limiting amino acids in corn equal to the levels in opaque-2 or floury-2 responded to amino acid supplementation in all trials, but performance was inferior to that obtained with the opaque-2 or floury-2 corn diets. When opaque-2 and normal corn diets were supplemented so both corn diets would have equal and adequate amounts of lysine and tryptophan, pig performance was the same with both opaque-2 and normal corn, suggesting that levels of available lysine and tryptophan are the major factors influencing the superiority of opaque-2 corn protein. Supplementation of normal corn with all essential amino acids equal to the levels in opaque-2 corn failed to produce as great a response as opaque-2 corn. When additional nonessential nitrogen was added to both normal and opaque-2 corn diets which were supplemented so both corn diets would have equal and adequate amounts of all essential amino acids, only those pigs fed the opaque-2 corn diet were responsive to the additional nonessential nitrogen.

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