Abstract The purposes of the present study were to iden-tify the correlation of total calcium (TCa) with albumin and total protein (TPro) in normal, hypoproteinemic and/or hypocalcaemic cows and to determine the usefulness of adjusted Ca formulas in assessing Ca levels in hypopro-teinemic and/or hypocalcaemic conditions. Two hundred and nineteen clinically healthy Holstein dairy cows were selected from 15 herds. Another 51 Holstein cows up to 48 h after parturition were sampled. Ten out of these cows developed parturient paresis. Serum Ca, albumin and TPro concentrations were measured using automated biochem-ical analytical techniques. Results were analysed by Student’s t test, Pearson’s correlation coefficient test and regression analysis. TCa concentration correlated with the concentrations of albumin (r =0.53, p<0.001) and TPro (r =0.603, p<0.001) in the serum of 219 lactating cows. Two correction formulas for Ca were derived on the basis of concentrations of albumin and TPro: (1) adjusted Ca by albumin (mmol/L)=measured serum TCa (mmol/L)−0.02 serum albumin (g/L)+0.78; (2) adjusted Ca by TPro (mmol/L)=measured serum TCa (mmol/L)−0.015 serum TPro (g/L)+1.2. The results indicate that TCa does not reflect the true Ca situation of the body in hypoproteinemic conditions and adjusted formulas may be appropriately used to correct TCa. In hypocalcaemic and normopro-teinemic conditions (such as parturient paresis in cattle),TCa and adjusted Ca values correctly reflect the true Ca situation of the body.

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