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Threonine as the second limiting amino acid in barley for rowing-finishing pigs and growing rats Aw-yong, Lai Mon

Abstract

Supplementation with graded levels of threonine to an all barley-lysine diet (0.75% total lysine) improved the daily gain, feed efficiency and carcass quality of growing-finishing pigs. An addition of 0.10% threonine produced the optimum growth response in the experimental animals. No additional improvement was obtained with higher levels of threonine or threonine plus methionine supplementation of the diet. The 0.10% level of threonine supplementation gave performance criteria which were comparable to those obtained with the barley-soybean control diet, except the former diet resulted in significantly higher backfat measurements. Threonine added at levels of 0.15% resulted in higher nitrogen retention than the other barley-lysine-threonine diets. Nitrogen retention on this diet did not differ significantly from the control diet. Barley-amino acid diets resulted in better protein ultilization than barley-soybean control diets. Feeding trials and metabolism trials indicated that methionine was not limiting in barley and that threonine was the second limiting amino acid. Growth trials with weanling rats confirmed the results obtained in the pig nutritional experiments. Rat experiments indicated that no additional beneficial effects were obtained when lysine levels were increased from 0.75% to 0.90% even when supplemented with additional threonine. Results indicated that supplementation with lysine to a total level of 0.75% and threonine at a level of 0.10% resulted in a highly balanced amino acid ratio for rats, and gave growth rates which approached those obtained on the control diet. Supplementation of the barley-lysine diet with 0.20% threonine and all other essential amino acids resulted in growth rates and nitrogen retentions which resembled the results obtained with the control diet. The replacement of the essential amino acid mixture with glycine on an equal nitrogen basis did not result in adequate nitrogen retention or growth rates.

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