Growth and nitrogen balance studies with growing pigs fed on diets containing normal oropaque-2 maize, meat and hone meal, and synthetic amino acids

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Abstract
Two experiments were conducted with pigs of 23-50 kg body weight to examine growth (experiment 1) and N retention (experiment 2) supported by diets based on either normal maize or opaque-2 maize each containing meat and bone meal as the only source of supplementary protein and the orders in which essential amino acids are limiting in these diets. Sixteen diets were formulated in a 24 factorial arrangement, the factors being maize type and added lysine, tryptophan and methionine. Diets contained comparatively low concentrations of crude protein and high concentration of nicotinic acid. Diets based on opaque-2 maize promoted much faster and more efficient growth than those containing normal maize, which primarily reflected the higher tryptophan content of the mutant. From the significant main effects and interactions on rate of gain, feed conversion ratio and N retention; tryptophan and lysine were apparently the 1st and 2nd limiting amino acids, respectively, in both the normal maize and opaque-2 maize diets. Methionine may have been marginally 3rd-limiting in the opaque-2 maize diet, but it did not seem to be limiting in the normal maize diet, although it was 1 of the more limiting amino acids.