Purine derivatives excretion in lactating ewes fed straw diets with different levels of fish meal

Purine derivatives (allantoin, uric acid, xanthine and hypoxanthine) concentration in blood, urine and milk samples, from a group of 20 lactating ewes, were analysed by high performance liquid chromatography (HPLC). The mammary gland contributed, together with the kidney and salivary glands, to purine derivative (PD) excretion. Daily excretion of PD and allantoin in milk were 280 ± 22.9 and 178 ± 10.7 μmol day−1, respectively, representing 2.2 ± 0.16 and 1.6 ± 0.10% respectively of the total (mammary plus renal) excretion. Problems with the endogenous uric acid contribution of the mammary gland to milk PD excretion are discussed. Measurements of PD losses in milk would improve the efficiency of response models relating duodenal flow of purine bases with urinary excretion of PD, although milk PD excretion in ewes does not seem to be a reliable alternative to such methodologies.