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Niacin-Replacing Value of L- and DL-Tryptophan in Chick Diets as Influenced by Carbohydrate Source¹

Department of Poultry Husbandry, University of Maryland, College Park

L- and DL-tryptophan were compared with respect to their ability to replace niacin in the diet of the chick. The L-isomer appeared to be the only one utilized by chick tissues. This isomer was found to be approximately twice as active as DL-tryptophan when the diet contained glucose as the source of carbohydrate. When starch replaced glucose in the diet, the D-tryptophan was of some value. The difference in value of the D-tryptophan when starch was substituted in place of glucose is believed to be the result of a change in the bacterial flora of the digestive tract. The value of the D-tryptophan was decreased by the addition of sulfasuxidine to the diet.

Replacing the glucose of the diet by starch decreased the growth rate except when niacin was added. Chicks fed niacin-adequate diets containing added sulfasuxidine grew more rapidly than those fed the same diet without sulfasuxidine.

² Present address: Merck and Co., Inc., Rahway, N. J.

³ Present address: Poultry Division, University of Minnesota, St. Paul.

Manuscript received 3 July 1950.