Utilization of dietary purines and pyrimidines by non-ruminant animals.

Introduction Interest in the nutritional significance of dietary nucleic acids and their constituent purine and pyrimidine bases dates back to 1937 when Frost & Elvehjem ( I 93 7) demonstrated the beneficial properties of exogenous nucleotides given to rats fed on low-niacin diets. The early work formed part of the search for unidentified growth factors (UGF) in various dietary ingredients including fish solubles, whey and yeast (Barnett et al. 1956; Eyssen, 1962). With the advent of large-scale production of single cell protein (SCP) in recent years, interest in nucleic acid metabolism has been revived by claims that the purine and pyrimidine nucleotides in SCP may be salvaged and re-utilized for growth and nitrogen retention by non-ruminant animals. There is some evidence that small SCP inclusions in pig and poultry diets improve N retention (D’Mello & Acamovic, 1976; D’Mello et al. 1976) and this effect is occasionally attributed to the utilization of the nucleic acid fraction (Whittemore et al. 1978). On the other hand, there have been claims that nucleic acids from SCP are almost completely catabolized by the pig and, therefore, not retained for tissue synthesis (Newport & Keal, 1980). This appears to be an opportune moment to review the metabolism of nucleic acids in non-ruminant animals.