J . Sci. Food Agric. 1979, 30, 381-387

Purine and Pyrimidine Utilisation by Chicks Fed Nitrogen-limiting Diets J. P. Felix D’Mello Department of Agricultural Biochemistry, Edinburgh School of Agriculture, West Muins Road, Edinburgh EH9 3JG

(Murruscr&t received 13 September 197%)

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-l D M 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. I n 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-l 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. 1. Introduction

Animals fed on diets containing hydrocarbon-grown yeasts and bacteria may consume substantial quantities of nitrogen (N) in the form of nucleic acids. It has been suggested that the constituent purine bases in these nucleic acids may be salvaged and utilised for nucleotide and nucleic acid synthesis in animal tissues.1-3 There is evidence that these bases may also serve as sources of N for the biosynthesis of the dispensable amino acids under conditions of dietary limitation of these amino acids.4 Excessive intakes of nucleic acids, on the other hand, may precipitate adverse effects in animals and there is evidence that certain purines can reduce growth rates when administered at relatively high dietary concentrations.2.4 The experiments reported here were conducted in order to examine the responses of young chicks to different combinations of purines and pyrimidines under conditions of severe dietary restriction of the dispensable amino acids. The purine and pyrimidine bases tested were those normally found in yeast and bacterial nucleic acids.

2. Experimental 2.1. Conduct of experiments The pre-experimental management of the male broiler chicks used in the current investigations 0022-5142/79/0400-0381 $02.00 01979 Society of Chemical Industry 381

J. P. F. D’MeIlo

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has been described elsewhere.5In each experiment, 16 chicks (in four replicate groups of four chicks) were assigned, at random, to each treatment on the seventh day of life and fed the experimental diets for a period of 14 days in experiments 1 and 3, and 11 days in experiment 2. At the termination of experiments 1 and 2, animals were starved for 12 h, killed by cervical dislocation and sealed within two polyethylene bags. The carcasses were stored at - 20°C. In order to calculate efficiencies of deposition of N and gross energy (GE) in the carcass during the experimental period, a number of chicks were killed and frozen, as described above, at the beginning of each experiment on day 7, post-hatching. All experiments were of the randomised block design.

2.2. Diets Semi-purified diets in ground, unpelleted form were used in all experiments (Table 1). The batches of maize meal and soya-bean meal were analysed for amino acids by automatic ion-exchange chromatography6 and the values so obtained were used to calculate the amino acid content of the basal diets. Different batches of maize were used in the three experiments. Deficiencies of the indispensable amino acids in these ingredients were made good by appropriate supplementation with crystalline amino acids to levels similar to those recommended by the Agricultural Research Council (1975).7 The final total dietary concentrations of each indispensable amino acid in the basal diets are shown in parentheses in Table 1. All basal diets were therefore designed to be limiting only in the content of dispensable amino acids. In experiment 1 the treatments consisted of supplementing the basal diet I, containing 19.84 g N kg-l dry matter (DM) with adenine, uracil, adenine+uracil and glutamic acid. Each supplement or combination of supplements provided an additional 2.33 g N kg-1 diet. Supplemented diets were thus equinitrogenous but higher in total N content than the unsupplemented basal diet. In the second experiment, the basal diet I1 containing 23.36 g N kg-1 DM (Table 1) was supplemented with guanine; thymine; guanine thymine; uracil thymine; uracil adenine; uracil

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Table 1. Composition of basal diets Experiment

Ingredients (g kg-l) Maize meal Sucrose Maize oil Minerals and vitamins” Soya-bean meal L-Threonine Glycine L-Valine L-Cystine DL-Methionine L-Isoleucine L-Leucine L-Tyrosine L-Phenylalanine L-Lysine. HC1 L-Histidine. HCI- HzO L-Arginine HCI L-Tryptophan Nitrogen content ( g kg-1 D M ) Metaholisable energy content (MJ kg-I D M ) I

a

See text for details of mixtures used.

1 Basal I

754.0 85.5 50.0 56.0

5.6

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4.8

2.4 3.7 4.3 2.7 4.3 4.9 9.8 2.6 8.1 1.3 19.84 16.66

(9.0)b (2.8) (9.0) (3.9) (5.6) (7.3) (11.2) (7.8) (9.0) (11.2) (4.5) (11.2) (2.2)

2 Basal I1 693.0 107.4 36.5 43.5 90.0 3.0 -

2.1

-

5.0 2.9

4.4 6.0 1.9 3.6 0.7 23.36 16.70

3

Basal 111 754.0 105.7 50.0 43.5

(7.4)* (4.9) (8.0) (1.7) (7.2) (7.4) (11.4) (4.2) (10.3) (10.3) (4.6) (10.3) (2.1)

4.2

3.8 -

5.5 4.3 2.5

-

7.2 8.6 2.7 6.9 1.1 18.89 16.77

(7.2)’’ (2.9) (7.7) (1.2) (7.4) (7.2) (11.0) (2.8) (11.3) (9.9) (4.4) (9.9) (2.0)

* Values in parentheses represent total concentrations (g kg-1 DM) of each amino acid i n basal diets.

Purine and pyrirnidinc utilisation

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adenine guanine thymine; uracil adenine guanine cystosine; uracil adenine guanine + cytosine+ thymine; and glutamic acid. The dietary levels of the various purines and pyrimidines and of glutamic acid were adjusted so that the total N contents of each supplemented diet were raised by 2.33 g N kg-1 diet. The basal diet I11 used in the third experiment was similar to that used in experiment 1. Supplements to diet TI1 consisted of uracil + adenine + guanine; uracil + adenine + guanine + cytosine; and glutamic acid. The dietary treatments raised the N level of each supplemented diet by 2.33 g N kg-l diet. When given in combination, the dietary levels of each purine and pyrimidine were adjusted so that each supplied an equal quantity of N with the total contribution of all components adding up to 2.33 g N kg-1 diet. In all experiments additions of purines, pyrimidines and glutamic acid were accomplished at the expense of sucrose. The mineral and vitamin mixture used in the preparation of basal diet I has been described in an earlier paper.5 The mixture used in diets IT and 111 represented a minor modification of one used in a previous investigation.8 The modifications consisted of the inclusion of thiamine-HC1, pyridoxine HCI, D-biotin, meso-inositol and p-aminobenzoic acid to provide final dietary levels of 10, 6, 0.6, 100 and 2 mg kg-1 diet respectively. Experimental diets were offered ad libitum. 2.3. Techniques Details of the preparation of carcasses prior to chemical analysis are given elsewhere.5The methods of analysis have also been outlined in that paper.5 3. Results 3.1. Experiment 1 Supplementation of basal diet I with adenine or uracil did not significantly (P>0.05) influence weight gain or efficiency of food conversion of chicks (Table 2). However, dry matter intakes were markedly reduced (P< 0.05) by adenine supplementation. Combined additions of adenine and uracil to diet I significantly enhanced growth rates (P

Purine and pyrimidine utilisation by chicks fed nitrogen-limiting diets.

J . Sci. Food Agric. 1979, 30, 381-387 Purine and Pyrimidine Utilisation by Chicks Fed Nitrogen-limiting Diets J. P. Felix D’Mello Department of Agri...
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