Meta-analysis of nutritional risk factors for milk fever in dairy cattle.

Data from 75 published trials were analyzed using meta-analysis techniques (pooling of data from many trials into one analysis) to determine nutritional risk factors for milk fever. Trials included in the analysis represented 1165 cows, 214 of which developed milk fever. Prepartum dietary concentrations of S and dietary anion-cation balance [(Na + K) - (C1 + S)] were the two nutritional factors most strongly correlated to the incidence of milk fever. Logistic regression analysis revealed that dietary S had the greatest influence on the incidence of milk fever. Increasing dietary S concentrations lowered the odds ratio of developing milk fever. Increasing dietary Na and CP increased odds ratios, but to a lesser extent. Relationship of dietary Ca to milk fever was nonlinear; relative risk of milk fever was greatest at 1.16% dietary Ca (DM basis) and was lowered as dietary Ca deviated either direction from 1.16%. Except when dietary Ca was extremely high or low, effects of changes in dietary Ca on the risk of milk fever were minor. Results of the analysis clarified the influence of Ca on the relative risk for milk fever and supported the theory that anion-cation balance exerts a strong, linear effect on the incidence of this disorder.