Nutritive value of D-tryptophan for the growing pig

The replacement value of D-tryptophan (D-TRP) for L-tryptophan (L-TRP) was estimated in four 28-d experiments with weanling pigs. In all experiments, supplementing TRP-deficient diets with D- and L-TRP significantly increased feed intake, rate and efficiency of gain and decreased plasma urea N (PUN). In Exp. 1, the performance responses to added D-TRP were similar to those with added L-TRP. Relative responses (D-TRP/L-TRP) for average daily feed intake (ADF), weight gain (ADG) and gain/feed (G/F) on percentage added TRP, and ADG on daily TRP intake were 1.2, 1.1, 1.0 and .9, respectively. In Exp. 2, pigs fed added L-TRP consumed more feed (P less than .05) and gained weight faster (P less than .05) than those fed added D-TRP. Relative responses of D- to L-TRP for ADF, ADG and G/F on percentage added TRP and ADG on daily TRP intake were .7, .7, .8 and 1.0. In Exp. 3, a 2 X 3 treatment arrangement was used. Pigs were fed two basal diets (.10% TRP) or basal diets with .05% added D- or L-TRP. The basal diets were formulated at two levels of large neutral amino acids (LNAA). The addition of L-TRP, as compared with D-TRP, increased ADF (P less than .01), ADG (P less than .01), G/F (P less than .05) and plasma TRP (P less than .01). Added LNAA decreased (P less than .05) ADF and added TRP increased G/F more in pigs fed high-LNAA diets than in those fed low-LNAA diets (interaction, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)