MAMMARY EPITHELIAL-CELL TIGHT JUNCTION INTEGRITY AND MAMMARY BLOOD-FLOW DURING AN EXTENDED MILKING INTERVAL IN GOATS

The timing and relation of changes in mammary epithelial cell tight ju nction integrity and mammary blood flow during a 36-h milking interval were studied in six lactating Saanen goats. An increase in lactose co ncentration in plasma, a decrease in transepithelial potential differe nce, and changes in ionic milk composition were used to indicate tight junction patency. After 36 h of milk accumulation, mammary tight junc tions had become disrupted. Further analyses indicated that this disru ption began after 21 h of milk accumulation and that mammary blood flo w also started to decline after 21 h. The time when both events occurr ed was not significantly different from the time when milk secretion b egan to decline (19 h). Moreover, positive but nonsignificant coffelat ions existed between these events. Mammary tight junctions became disr upted when milk secretion declined, suggesting that impairment of mamm ary tight junction integrity is associated with decreased milk secreti on during an extended milking interval. The decline in mammary blood f low may be the result of a negative feedback response to a reduced dem and for metabolites, which is due to a reduced rate of milk secretion.