Effect of drying off practices on mastitis infection.

Two methods of drying off cows, intermittent milking and abrupt cessation, were studied with data from 9254 quarters of cows on 36 New York dairy farms. Eighty percent of the cows were infused with nine different antibiotic preparations separately at drying off, and 20% served as controls. Cows dried off by intermittent milking has a similar number of quarters infected at drying off, had fewer spontaneous recoveries, had a higher rate of cure, and developed fewer new infections in control quarters in comparison with cows dried off by the stop method. Methods worked equally well in treated cows. However, intermittent milking resulted in fewer infections at subsequent calving than stop milking in nondry treated cows. Cows producing less than or equal to 4 kg of milk at drying off were more highly infected than higher producing cows. Hind quarters contained more infections at drying off, fewer responded to therapy, and more infections developed in the dry period. Cows with dry periods of less than or equal to 30 days had more infected quarters respond to therapy and had the fewest new infections in the dry period. The role of routine dry cow therapy in decreasing the number of infections in dairy herds by preventing new infections and removing old infections is demonstrated.