Three cattle calves (Bos taurus) and three buffalo calves (Bos bubalus) were weaned after receiving colostrum and then reared on bottle-fed milk. During the first month the animals did not have access to solid food. Urinary purine derivative concentration (PD), basal PD excretion and glomerular filtrate rate (GFR) were determined during fasting and feeding. After 1 month the animals were given access to solid feed (urea-treated rice straw 80% and molasses 20%) to stimulate rumen development. At 3 months of age, while the solid food was given, urinary PD, basal PD excretion and GFR were again determined.

Urinary PD excretion both during fasting and milk feeding did not differ significantly between buffaloes and cattle during the milk-feeding period (P > 0.05), but there were highly significant (P < 0.01) differences between cattle and buffaloes after 3 months of age and 2 months of access to solid feed (P < 0.01). The GFR was lower in buffaloes than cattle in both the milk-fed and solid-feed periods (P < 0.05).

It is suggested that the differences between buffaloes and cattle are due to differences in GFR as PD will stay longer in the blood and thus provide a greater possibility for recycling to the rumen. This, however, needs further confirmation. Whether permeability of PD from blood to rumen is an additional factor is not known.