THREONINE AS THE SECOND LIMITING AMINO ACID IN PEACE RIVER BARLEY FOR GROWING–FINISHING PIGS AND GROWING RATS

Abstract

Barley–lysine diets (0.75% total lysine, 0.37% threonine) with or without additional threonine and methionine were compared with a barley and 15.6% soybean meal control diet in a growth trial with 108 pigs and a metabolism trial with six collection periods per diet. Addition of threonine to the barley–lysine diet improved daily gain, feed efficiency and carcass quality, with the growth results obtained with the 0.10% threonine addition equalling those of the barley–soybean meal diet, except for backfat thickness, which was lower on the soybean meal diet. Nitrogen retention, however, increased up to the maximum level (0.15%) of threonine inclusion, when retention equalled that of the control diet. Addition of 0.10% methionine to the barley diet containing added lysine and threonine resulted in no responses. Growth and balance trials with weanling rats in general confirmed results obtained with the pigs. No additional beneficial effects were obtained when lysine levels were increased from 0.75 to0.90%, even when supplemented with additional threonine. However, in order to obtain results similar to those obtained on the barley–soybean meal diet, threonine additions to the barley had to be increased to 0.20% (0.57% total threonine) with the addition of a mixture containing other essential amino acids. Replacement of the essential amino acid mixture with glycine on an equal nitrogen basis did not produce adequate nitrogen retention or growth rate.