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The Addition of Glutamic Acid or Protein to a Threonine-Deficient Diet Differentially Affects Growth Performance and Threonine Dehydrogenase Activity in Fattening Pigs^1,2,

INRA, Station de Recherches Porcines, St-Gilles, 35590 L'Hermitage, France

The effects of dietary levels of threonine, protein (essential and nonessential amino acids) and glutamic acid (nonessential amino acid) on growth, food intake and threonine metabolism were studied in 54 fattening female pigs (Piétrain 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 limited and an adequate supply for growth, and three types of nitrogen supply: a basal diet supplying 12.6 g crude protein/100 g, a second diet 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 modify growth performance but increased L-threonine-3-dehydrogenase (TDG) activity when pigs were fed the higher threonine diet. The addition of L-glutamic acid to the threonine-deficient diet improved growth performance, but there was no effect at the higher level of threonine. Glutamic acid increased TDG activity in pigs fed the low threonine diet. We conclude that glutamic acid may have a sparing effect on threonine when threonine is rate-limiting for protein deposition, but the mechanism of the interaction between the two amino acids remains unknown.

KEY WORDS: • threonine • metabolism • L-glutamic acid • pigs • threonine dehydrogenase

¹ Presented in part at The First Anglo-French Symposium on Human and Animal Nutrition (The Nutrition Society and Association Française de Nutrition), September 9–11, 1992, Rennes, France [Le Floc'h, N., Sève, B. & Henry, Y. (1993) Threonine dehydrogenase (EC 1.1.1.103) in growing pigs fed a threonine deficient diet. Proc. Nutr. Soc. 52: 171A (abs.)].

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 11 November 1993. Revision accepted 22 April 1994.