Measurement of the quantity of lactose passing into mammary venous plasma and lymph in goats and in a cow

Summary Lactose in the plasma of 12 lactating goats and one cow with healthy udders has been measured by a sensitive and specific enzymic assay. Mean values (±S.E.) for arterial and venous concentrations were 52±11 µM and 70±11 µM respectively. Simultaneous measurement of mammary blood flow, milk yield and milk lactose concentration showed that 2·70±0·25% (mean±S.E.) of the total lactose production passed into the plasma. This rose to 42·7% in a goat when milking was suspended for 46 h. No lactose was found in the plasma of male and non-lactating female goats, but it was detected 4 days before parturition in a nulliparous goat.