A RANDOMIZED BLIND TRIAL ON DRY COW ANTIBIOTIC INFUSION IN A LOW SOMATIC-CELL COUNT HERD

The objective of the study was to evaluate the effect of administratio n of antibiotics to cows at dry-off in a low SCC herd. Cows were infus ed at dry-off with an intramammary antibiotic on the left or the right side of the udder. Selection of the infused quarters was random, and all people evaluating the occurrence of mastitis were unaware of which half of the udder was infused. The quarters that were infused with an antibiotic showed a significantly lower incidence of clinical mastiti s in the dry period. Quarters that were uninfused had 10 cases of clin ical mastitis versus 1 case in quarters that were infused with antibio tics. The quarters that were infused showed a reduction of minor patho gens at calving. The uninfused quarters showed little evidence of spon taneous cure during the dry period. Milk leaking was frequent during t he drying off period. Milk leaking was also associated with the occurr ence of clinical mastitis later in the dry period. Cows that leaked mi lk had a four times greater risk of clinical mastitis in the dry perio d.