Short communication: Effects of isolation stress on mammary tight junctions in lactating dairy cows

Eighteen cows had been selected for their responsiveness to psychological s tress during the first lactation and were classified as having low (n = 10) or high (n = 8) cortisol concentrations in response to isolation-induced s tress. In the present study these cows, now in their second lactation, were used to determine the effect of social isolation stress on the permeabilit y of mammary tight junctions. During the experiment, each cow was isolated from the rest of the herd for 55 h. After the 1st h of isolation, each cow received a bolus infusion of endotoxin in one hind quarter in order to chal lenge tight junctions. Blood samples were taken throughout to measure lacto se, which was used as an indicator of tight-junction leakiness. After 1 h o f isolation, stress caused an increase in tight junction permeability in bo th groups, which was further enhanced by the endotoxin treatment. Although the permeability did not differ significantly between the two groups, it wa s consistently higher in the high-cortisol group, which was also the most s tress-responsive group. Thus, psychological stress may adversely affect mil k quality by allowing serum components to leak into milk.