Sources of variation in milk osmolality in dairy cows

= 0.02) osmolality (301 ± 1 mOsm/kg) than Swedish Holstein cows (299 ± 1 mOsm/kg). The observed differences range from 1% to 9% with variations between breeds being the smallest and those between months/lactation stages and individuals being the largest. It is concluded that there are variations in milk osmolality between individuals, days and breeds that exceed what can be interpreted as thirst-stimulating (+1-2%). Since the variation among clinically healthy animals and over time is considerable, there is potentially a challenge to the practical use of milk osmolality as an indicator of hydration state to be of practical use. Further studies are needed to understand the variations in milk osmolality when cows are water deprived.