The effects of age on the erythrocyte sodium and potassium concentrations of dairy cows during late pregnancy and early lactation.

Blood samples were taken at weekly intervals from 54 dairy cows (mainly Friesians and Jerseys) during the periods 8 weeks before and 8 weeks after calving. The cows were divided into two age groups; group 1 consisting of 26 cows aged 2 1/2 years and group 2 consisting of 28 cows aged 5-9 years. The changes in the erythrocyte sodium (ENa) and the erythrocyte potassium (EK) concentrations before and after calving were expressed as the slopes for each component regressed on weeks. In the older cows the concentration of ENa decreased (p less than 0.05) while that of EK increased (p less than 0.05) after calving. Both the ENa and EK concentrations varied significantly (p less than 0.01) between cows in the two age groups. The prepartum and postpartum ENa and the postpartum EK concentrations varied significantly (p less than 0.05) between weeks. EK type did not influence the changes in ENa or EK concentrations before or after calving.