Organic farms tended to have older cows than conventional herds, and in the statistical models, the lactation category was a significant explanatory variable for all three diseases studied. As shown in Figures 1 through 3 (cumulative risk rates), and Tables 2 through 5 (relative odds ratios), the risk of disease increased with lactation number. This observation is valid for both organic and conventional dairy husbandry, and is in agreement with results from the Norwegian population (Østera°s and Spanne, 1999).