Abstract
Three experiments were conducted to determine how dietary protein and tryptophan influence the lipid metabolism of growing broiler chicks. A diet-dilution method (corn-com gluten meal-gelatin summit/corn starch basal) was used in three factorial experiments. Various levels of protein and tryptophan were fed in each experiment: protein from 16 to 28% and tryptophan from .34 to 2.74% of protein.Gain was maximized when the dietary levels of tryptophan were .83 ± .03, .77 ± .04, .77 ± .05, and .78 ± .05% of the protein for 16, 20, 24, and 28% dietary protein, respectively. The requirement estimates for feed efficiency and gain were similar. Liver lipids significantly decreased as the level of dietary tryptophan increased at each protein level (P<.0001). Dietary tryptophan did not significantly alter the concentration of total plasma lipid in the chicks or in die carcass lipid content (P>.2399). Tryptophan supplementation significantly increased the concentration of plasma linoleic acid and plasma free tryptophan.The requirement of the chicks for tryptophan was estimated to be .80 ± .01% of the dietary protein for the growing chick. Increased liver lipid and decreased plasma tryptophan are diagnostic lesions suggesting a tryptophan deficiency.
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