Effects of dry period length on clinical mastitis and other major clinical health disorders.

Four, 7-, and 10-wk dry periods were randomly assigned to 366 dairy cows in eight herds. A multiple polytomous logistic regression analysis was conducted with the objective to reveal possible important effects of the dry period on the risk of contracting major clinical health disorders. Several complex statistical interactions were revealed. Complications around and after drying off occurred least frequently at 7-wk dry periods. There was little evidence of an effect of the dry period on the risk of clinical mastitis and other severe clinical disorders around and after calving. With short calving intervals, the risk of occurrence of complications at calving decreased with the length of the dry period. This relation was reversed at longer calving intervals. Dry period lengths of approximately 7 wk appear to be associated with the lowest risk of clinical health disorders, but other factors like milk yield at drying off and previous mastitis are much more important predisposing factors.