Effects of dietary cation–anion differences on serum calcium, phosphorus and magnesium concentrations in periparturient dairy cows

The aim of this study was to investigate the influence of two dietary cation-anion differences (DCAD) on the serum calcium, phosphorus and magnesium of forty dairy cows directly endangered by parturient paresis. The cows were chosen from three farms where, altogether, 736 Friesian dairy cows were bred. They were divided randomly into two groups. The control - cation group (n = 15) received a ration with an average DCAD of 243 ± 132 mEq/kg and the experimental - anion group - (n = 25) received a ration with an average DCAD of -28 ± 136 mEq/kg of DM. We found that when the calcium levels in the sera of the experimental group were compared to those of the control group they were statistically significantly higher (P = 0.0095) two days prior to parturition. They were also higher the day before (P = 0.0007) and two days after (P = 0.0296) parturition, which confirmed the positive effects of an anionic diet on the mechanisms regulating calcium's absorption from the intestine and its mobilization from the bones during the most critical days immediately before and after parturition. The anionic salts supplement had no significant statistical affect on the level of serum phosphorus and magnesium. However, the expected decrease of the phosphorus level that occurs around the parturition period was established in both groups of caws, though the mean values of these blood elements were at an adequate level throughout the experiment. Five cows were affected by parturient paresis: two (13.3%) from the controls and three (12.0 %) from the experimental group. The occurrence of the disease was confirmed by serum analyses which showed that the affected animals had statistically significant lower calcium (P = 0.0332) and phosphorus (P = 0.0411) concentrations in comparison with clinically normal animals. Considering the analyses of the ration and the fact that all the cows developed the disease after parturition, it is our opinion that the major cause for the occurrence of the disease in the group fed anionic salts was an insufficient calcium intake after parturition.