Utilization of D- and L-tryptophan by the growing dog

Two 4 x 4 Latin square experiments were conducted with English Pointer puppies to determine the growth promoting capacity of D-tryptophan (trp) relative to L-trp and to estimate the trp requirement of the growing dog. Based upon a multiple linear regression slope-ratio technique, D-trp had an efficacy value of 35.5 +/- 6.4% relative to L-trp. The urine of dogs fed D-trp contained 14.6% of the ingested trp; no measurable trp was recovered in the urine of dogs fed L-trp. The trp requirement for maximal weight gain was at least .16% for 6-to 10-wk-old dogs, between .12 and .16% for 10- to 12-wk-old dogs and less than or equal to .12% for 12- to 14-wk-old dogs. The overall requirement for the 6- to 14-wk age period was .15%. Total N, as well as urea-N, in urine decreased and N retention increased with increasing levels of dietary L-trp; NH3-N, creatinine-N and fecal-N were unaffected by treatment.