The effect of age on erythrocyte magnesium concentrations of dairy cows during late pregnancy and early lactation.

Blood samples were taken at weekly intervals from fifty four 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 2 1/2 to 4 years old and Group 2 consisting of 28 cows over 4 years old. The changes in erythrocyte magnesium (EMg) and plasma magnesium (PMg) concentrations before and after calving were expressed as the slope of each blood parameter regressed on weeks. The post-partum EMg concentration slope (increase) was greater (P less than 0.05) in the older cows than in the young ones. The older cows also had higher (P less than 0.05) mean EMg concentrations than the young cows. Between cow EMg concentrations variations were significant (P less than 0.05) in both age groups while the weekly EMg concentration variations were only significant (P less than 0.05) in the older cows after calving. Age did not influence the changes in PMg concentrations before or after calving. Nor did the PMg concentrations vary significantly either between cows or between weeks.