Efficiency of Tryptophan as a Niacin Precursor in the Young Chick

Abstract

Three assays involving 539 8-day old crossbred chicks fed a completely purified diet were conducted to establish the efficiency in vivo of converting tryptophan to niacin. In the first assay the requirement for L-tryptophan was found to be 1,300 ppm in the presence of excess (100 ppm) dietary niacin. Next, the niacin requirement was determined in chicks fed 1,300 ppm L-tryptophan. It was established that 20 ppm niacin permitted maximal rate and efficiency of weight gain and completely prevented incidence of a tongue and mouth lesion. The final assay showed that chicks fed a niacin-free diet with 1,300 ppm tryptophan responded equally well to either 900 ppm supplemental L-tryptophan or 20 pm supplemental niacin. Hence 45 ppm tryptophan was equivalent to 1 ppm niacin, indicating an efficiency of conversion of tryptophan to niacin of about 2%.