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Nutritive Value of D-Tryptophan for the Growing Pig¹

Iowa Agriculture and Home Economics Experiment Station, Ames 50011

Abstract

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<.05) and gained weight faster (P<.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<.01), ADG (P<.01), G/F (P<.05) and plasma TRP (P<.01). Added LNAA decreased (P<.05) ADF and added TRP increased G/F more in pigs fed high-LNAA diets than in those fed low-LNAA diets (interaction, P<.05). Relative responses of D- to L-TRP for ADF, ADG, G/F on percentage added TRP and ADG on TRP intake were .5, .5, .7 and .9. In Exp. 4, pigs fed supplemental D-TRP had higher (P<.01) plasma TRP than those fed added L-TRP. The relative responses of D- to L-TRP for ADF, ADG, G/F and ADG on TRP intake were .8, .8, .8 and 1.0. The data of Exp. 2, 3 and 4 indicate that supplemental D-TRP is about 70% as effective as L-TRP for increasing ADG, ADF and G/F of pigs fed low-TRP diets based on natural feedstuffs.

¹ Journal Paper No. J-10929 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 2356.

² Dept. of Anim. Sci.