EFFECTS OF FREQUENT MACHINE MILKING AND SUCKLING IN EARLY LACTATION ON BLOOD-PLASMA ION HOMEOSTASIS IN HIGH-YIELDING DAIRY-COWS

Groups of nine or ten cows were assigned, after calving, to treatments in which they were (i) machine milked three times daily (M3), (ii) ma chine milked six times daily (M6) or (iii) suckled three times daily i n addition to being machine milked three times daily (S). Treatments w ere administered during the first 6 weeks postpartum On one day, at we eks 1 and 6 postpartum, blood samples were collected from all cows at 30-min intervals between 06.00 and 13.00 h and these were analysed for plasma osmolality and plasma concentrations of Na+, K+ and Cl-. Milk yield was significantly higher in suckled cows than in cows milked six times daily, but significantly lower in cows milked three times daily . In cows milked six times daily, and to a greater extent in suckled c ows, there was a reduction in plasma osmolality and monovalent ion con centrations (Na+, K+ and Cl-), which could increase the susceptibility of the cows to water intoxication. Moreover, suckling or milking the cows six times daily was associated with increased fluctuations in pla sma osmolality and plasma Cl- concentrations. The decrease in plasma o smolality and ion concentration and the increased variation in plasma osmolality and Cl- were probably related to increased water intake and may be indicative of a severe challenge to homoeostasis regulation.