Purine and pyrimidine utilisation by chicks fed nitrogen‐limiting diets

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Abstract
The responses of chicks to purine and pyrimidine supplementation of diets severely limiting in the dispensable amino acids have been measured in three experiments. In experiment 1, combined additions of adenine and uracil to a diet with a nitrogen (N) content of 19.84 g kg−1 DM enhanced growth and dry matter intakes to levels similar to those attained by chicks receiving an equinitrogenous supplement of glutamic acid. Chicks in the latter group, however, had the best efficiencies of carcass N deposition. In experiment 2, growth, dry matter intakes and efficiency of food conversion of chicks fed a diet with 23.36 g N kg−1 DM were improved markedly by combined supplements of adenine, uracil, guanine and cytosine. Equinitrogenous inclusions of guanine; guanine with thymine; uracil with thymine; or uracil with adenine were ineffective. Efficiency of carcass N deposition declined appreciably on supplementing the basal diet with purines and pyrimidines in different combinations, appreciable reductions occurring with additions of thymine; uracil with thymine and uracil with adenine. The low N efficiencies observed in the last two groups were improved by combined additions of adenine, uracil, guanine and cytosine. The highest efficiencies of N utilisation occurred in chicks fed a glutamic acid supplement. In experiment 3, the simultaneous addition of uracil, adenine and guanine was as effective in stimulating the growth performance of chicks fed a diet with 18.89 g N kg−1 DM as a more complex mixture including cytosine. The best growth and efficiency of food conversion values were recorded in the group receiving supplementary glutamic acid.