Interrelationships among the length of milk stasis, tight junction permeability to lactose and monovalent cations, rate of milk secretion and composition in dairy goats traditionally milked once a day

• We evaluate the mammary tight junction (TJ) integrity in two dairy goat breeds.
• Our study has focused evaluating extended milking intervals.
• TJ permeability to lactose was much higher than to monovalent cations (Na+ and K+).

Canarian goats are well adapted to extended milkings. To gain more information on this adaptation, 32 dairy goats in mid lactation belonging to Majorera and Palmera breeds were subjected to milk stasis of 10, 14, 24 (the normal routine), 28 and 32 h; and milk volumes, milk composition, concentrations of Na+ and K+ in milk and blood plasma and plasma lactose were measured at each interval. The major findings were: i. Milk stasis did not induce changes in milk fat and milk protein secretion rates. In contrast, the extension of the interval between milkings was associated with a decrease of milk lactose secretion rate, ii. Comparison of the relative changes of Na+ and K+ in milk with blood and plasma lactose content indicates that the tight junction (TJ) permeability to lactose was much higher than to monovalent cations. It was concluded that an important element in the adaptation of Canarian dairy goats to extended milking intervals may be related to maintenance TJ resistant to paracellular leakage, particularly to passage of monovalent ions. Thus, the present study increases the understanding on adaptation of small ruminant to extended milking interval, which has been related so far to their high cistern storage capacity.