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Departmentof Nutrition, University of Guelph, Guelph, Ontario, Canada N1G 2W1
The tryptophan requirement of 2.5-kg piglets was measured by the oxidation of L-[1-14C]phenylalanine or DL-[1-14C]lysine when meals containing various levels of L-tryptophan were offered. Increasing dietary tryptophan from 0.65 to 2.0 g/kg decreased 14CO2 release from L-[1-14C]phenylalanine but further increases in dietary tryptophan level resulted in no further decrease in 14CO2 output. Regression analysis, with a crossover model, showed phenylalanine oxidation was minimized with a dietary tryptophan level of 1.94 g/kg (95% confidence limits 1.93 to 1.95). The oxidation of lysine was also reduced by increasing tryptophan levels to 2 g/kg; as tryptophan level was increased to 3 g/kg there was no statistically significant reduction of lysine oxidation. These studies suggest that the dietary tryptophan requirement of the 2.5-kg piglet is no more than 2 g/kg of a 240 g protein per kilogram diet.
KEY WORDS: • tryptophan • phenylalanine • lysine • piglet
1 Supported by the Natural Sciences and Engineering Research Council of Canada, and the Ontario Ministry of Agriculture and Food.
2 Presented in part at the AIN Graduate Student Competition, 67th Annual FASEB Meeting, Chicago, IL, April 1983. Fed. Proc. 42, 5971, 1983 (abs.).
3 To whom reprint requests should be sent.
Manuscript received 26 March 1984.
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