Dietary Amino Acid Balance in Growing-Finishing Pigs: Effect on Diet Preference and Performance1

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Abstract
The effect of dietary amino acid balance upon diet preference and performance of individually-fed pigs was studied in three experiments. A complete diet (A), an incomplete diet (deficient in several amino acids) (B) and a protein-free diet (C) were offered in four free-choice treatments: AA, AB, AC and BC choices. Pigs preferred the A diet in the AB choice (93.5 and 88.6%) and in the AC choice (69.1 and 63.1%) during the growing and finishing periods, respectively. Weight gain, feed intake and serum protein concentration were depressed only in the BC choice. The AC choice produced fatter carcasses than AA and AB choices. Pigs given the BC choice selected B diet 39.7 and 47.0% during growing and finishing periods, respectively. By replacing B by A diet in the choice growth-depressing effects were overcome but loin eye area remained smaller than in pigs in AA and AB. With finishing pigs using the same four treatments, results were similar to those with growing pigs except that in BC choice gain was less severely depressed, feed intake was not depressed and selection of B diet (61.2%) was greater, indicating that age has an effect on the acceptance of an amino acid imbalanced diet. It is concluded that: (1) pigs prefer an amino acid balanced diet to a diet of a similar protein level but with a deficiency of several amino acids, (2) choice between a protein-free diet and an adequate protein diet results in intake of sufficient protein for maximum weight gain but not for maximum carcass leanness, (3) growing pigs prefer a protein-free diet (which will not support life) to an incomplete protein with a deficiency of several amino acids (which will support life); finishing pigs appear to be less selective. Copyright © 1970. American Society of Animal Science . Copyright 1970 by American Society of Animal Science