Histidine, phenylalanine-tyrosine and tryptophan requirements for growth of the young kitten.

Growth assays were conducted to estimate the minimal dietary requirement levels of histidine, tryptophan, phenylalanine and tyrosine for the young kitten. Dietary concentrations of histidine and tryptophan of .30 and .15%, respectively, were found to support optimal kitten performance. A preliminary study of the total aromatic amino acid (TAAA) requirement indicated that no more than 1.20% TAAA (.60% phenylalanine + .60% tyrosine) is required by the kitten. Subsequent experiments revealed no decrease in growth rate when TAAA were reduced to 1.00% of the diet. At this level of TAAA, tyrosine could supply 50% of the requirement for TAAA.

Nitrogen requirement of the kitten.

Three experiments were conducted to determine the nitrogen (N) requirement of the young kitten. The feline basal diet contained minimal requirement levels of each indispensable amino acid (IAA) to comprise a total dietary N concentration of 2.52% and an IAA N to dispensable amino acid (DAA) N ratio (I/D) of 0.70. In experiments 1 and 2, both the dietary N concentration and I/D ratio were varied through changes in either the DAA level (experiment 1) or IAA level (experiment 2). The results revealed that a reduction in either dietary N or in I/D ratio from basal levels (ie, 2.52% N and I/D ratio of 0.70) depressed (P less than 0.05) kitten weight gain, feed efficiency, and N retention, whereas simultaneous increases in each resulted in no further improvement in these responses. Comparison of this feline basal diet with a commercial ration (experiment 3) revealed no differences (P less than 0.10) in gain, gain/feed, or N retention, although the purified diet showed superiority (P less than 0.01) when gain/N intake was determined (13.3 vs 5.7). Therefore, the feline dietary N requirement has been estimated to be 2.52% (15.75% protein equivalent) or 16% of the calories as protein. In the process of these experiments, creatinine and orotic acid excretion from kittens fed the purified diet were constant, averaging (+/- SEM) 24.7 +/- 0.7 mg/kg of body weight and 9.95 +/- 2.3 micrograms/mg of creatinine, respectively. Urea-N and ammonia-N comprised approximately 83.0% and 3.8% of the total urinary nitrogen.