Excretion of purine derivatives by ruminants: endogenous excretion, differences between cattle and sheep

The endogenous urinary excretion of the purine derivatives allantoin, uric acid and xanthine plus
hypoxanthine were measured in twenty-nine lambs, ten cattle (six steers, one cow and three preruminant
calves) and four pigs. The sheep and mature cattle were nourished by intragastric infusion and the calves
were given a milk-substitute. The pigs were fed on a purine-free diet. The excretion of total purine
derivatives was substantially greater by the cattle, being 514 (SE 20.6) pmol/kg live weight (W)’” per
d compared with 168 (SE 5.0) pmol/kg Wo7’ per d by the sheep and 166 (SE 2.6) pmol/kg WO” per d by
the pigs. Plasma from normally fed sheep, cows and pigs was incubated with either xanthine or uric acid.
Sheep and pig plasma had no xanthine oxidase (EC 1.2.3.2) activity whereas plasma from cattle did.
Uricase (EC 1 .7.3.3) was not present in plasma of cattle and pigs and appeared to be present in trace
amounts only in sheep plasma. It is suggested that the species differences in endogenous purine derivative
excretion were probably due to the different profiles of xanthine oxidase activity in tissues and
particularly in the blood. This is because a high xanthine oxidase activity would reduce the chance to
recycle purines, by increasing the probability of degradation to compounds which could not be salvaged.