Why do my calves have areas of hair loss with skin lesions?

Calves commonly become infected with ringworm fungus and wart virus. The two infectious, contagious conditions are easily recognized and differentiated by the gross appearance of the localized hair loss with skin lesions. In cases where the hair loss with skin lesions is generalized, other causes for consideration are photosensitization, dietary deficiencies, worm infections, and horn fly and lice infestations. Some common causes are ringworm fungus and warts.

Ringworm fungus (Dermatophytosis): The early stage of a fungus infection in the skin quite often goes unnoticed because of poorly visible small areas, slightly raised with roughened hair. Infected cows serve as common sources of the fungus that is transferred by direct contact to calves. After several weeks of the fungus infiltrating hair follicles, the hair falls out, leaving circumscribed grayish lesions. The scaly lesions, which coalesce to form large patches of hair loss at least 3 inches in diameter, are frequently located on the face and neck and are more common in young cattle. Although the infection tends to be self-limiting with spontaneous recovery after several months, affected calves should be separated and treated to prevent transmission to other calves.

Warts (Papillomatosis): Warts are fibrous tumors of the skin and mucous membranes and are caused by many strains of the papilloma virus. The virus is usually transmitted to calves by direct contact from infected cows. Transmission can also occur through contaminated instruments that puncture the skin and biting flies, such as horn flies and stable flies. The cauliflower-type growths occur primarily on the head, neck, and shoulders; in the mouth and vagina; and on the teats, vulva, and penis. To prevent transmission to other calves, isolate the calves with warts. Over a period of three to 12 months, the affected calves build immunity against the virus in the warts and skin. Once the immunity kills the viruses, the warts dry and slough off.