THE ADDITION OF GLUTAMIC-ACID OR PROTEIN TO A THREONINE-DEFICIENT DIET DIFFERENTIALLY AFFECTS GROWTH-PERFORMANCE AND THREONINE DEHYDROGENASE-ACTIVITY IN FATTENING PIGS

The effects of dietary levels of threonine, protein (essential and non essential amino acids) and glutamic acid (nonessential amino acid) on growth, food intake and threonine metabolism were studied in 54 fatten ing female pigs (Pietrain x Large White) from 40 to 100 kg live weight . Six experimental diets were compared using a 2 x 3 factorial design: two levels of threonine (0.42 and 0.52 g/100 g) corresponding to a li mited and an adequate supply for growth, and three types of nitrogen s upply: a basal diet supplying 12.6 g crude protein/100 g, a second die t providing additional protein to give a total supply of 15.6 g crude protein/100 g, and a third diet providing nonessential nitrogen in the form of L-glutamic acid to give the same total supply of 15.6 g crude protein/100 g diet. Protein addition to the basal diets did not modif y growth performance but increased L-threonine-3-dehydrogenase (TDG) a ctivity when pigs were fed the higher threonine diet. The addition of L-glutamic acid to the threonine-deficient diet improved growth perfor mance, but there was no effect at the higher level of threonine. Gluta mic acid increased TDG activity in pigs fed the low threonine diet. We conclude that glutamic acid may have a sparing effect on threonine wh en threonine is rate-limiting for protein deposition, but the mechanis m of the interaction between the two amino acids remains unknown.