Photosensitization Outbreak in Shorthorn Calves in Missouri

In 1989, an outbreak of photosensitization occurred in Shorthorn calves from three herds in Boone County, Missouri. In herd 1, three calves aged 3-4 weeks showed mild symptoms, including skin lesions on sparsely haired areas, slightly elevated gamma glutamyl transferase (GGT) activity, and bilirubin, indicating mild liver damage. These calves recovered within a week. In herd 2, eight calves aged 2-3 weeks exhibited more severe symptoms, such as flaking skin, hair loss, photophobia, diarrhea, and lesions on various body parts. Elevated GGT activity suggested biliary tree damage, but aspartate aminotransferase (AST) levels were normal. Recovery took about three weeks. Photosensitization, akin to severe sunburn, involves skin hyperreactivity to sunlight due to photoreactive molecules, leading to various biochemical and functional effects, including DNA and protein photoadduct formation, lipid peroxidation, and membrane protein photo-oxidation.