Mineral profile of blood plasma of lactating dairy cows.

Each of 20 Holstein cows was assigned randomly to a salt treatment upon calving. The experimental design was a 2 x 2 factorial having age (young versus mature) and salt treatment (plain versus mineralized) as factors. Salt was fed ad libitum. All animals were maintained on a balanced ration of corn silage fed ad libitum and concentrate fed in the barn in a ratio of .45 kg concentrate per 1.36 kg actual milk production. Concentrations in blood plasma of calcium, magnesium, sodium, potassium, cobalt, bicarbonate, chloride, phosphorus, total serum protein, sulfur, and fluoride were monitored throughout lactation and gestation. Statistical evaluation of weekly means for each treatment group for each element by analysis of variance showed when concentrations were different. Concentrations of calcium and magnesium were higher in younger animals than in mature animals during much of the lactation cycle. Magnesium concentration was higher in cows fed trace-mineralized salt. Concentration of phosphorus was higher in younger animals throughout the lactation cycle. Total serum protein was higher in mature cows throughout lactation, and concentrations of sulfur and fluoride were higher in mature cows through much of the cycle.