Digital dermatitis (DD) is a polybacterial disease that affects the skin on the heels of cattle. Round lesions occur along the coronary band of the claws, above the interdigital space next to the heel bulbs. It was first described in Italy in 1974 by Cheli and Morterallo, and it has become a growing problem worldwide for the dairy industry.
The bacteria most often associated with DD are spirochetes of the genus Treponema. Digital dermatitis is commonly treated with a topical application of tetracycline (paste or powdered form) directly to the lesion. Therefore, the risk of violative antibiotic levels in milk following topical application of tetracycline is high. The maximum residue limit for tetracycline in dairy milk is 100 ng/mL in the European Union and Canada, whereas in the United States the tolerance is 300 ng/mL. The Food Animal Residue Avoidance Databank recommends a 24-hours milk withdrawal interval for topical use of tetracycline in the United States.