Sunburn and Photosensitization

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Sunburn is injury to the skin caused by excessive exposure to the ultraviolet rays of sunlight. Pigs that are unaccustomed to direct sunlight may be sunburned if not exposed gradually to their outdoor environment. The white or light-colored breeds are more severely affected. Although suckling and weanling pigs are most likely to be affected, all age groups are susceptible. The ears and back get more direct exposure to sunlight and often are more severely sunburned. Sunburned skin is reddened, edematous, hot, and painful. Affected areas later appear roughened and may peel. A common clinical presentation of sunburned pigs is a brief “attack” of pain manifested as squealing or dipping the back while walking. In some cases, pigs may drop to their stomach, then get up and walk. Presumably, this is response to a feeling pain over the lumbar area. There have been reports of abortions associated with sunburn.

Photosensitization should be differentiated from sunburn. It occurs only in areas of white skin. Lesions result when pigs ingest, are injected with, or come into skin contact with a photodynamic agent and then are exposed to sunlight. Sunlight includes wavelengths that activate the photosensitization process. Photosensitizing agents are present in some pastures (alfalfa, clover, oats, rape, buckwheat, others). Also, several common pharmaceuticals (phenothiazine, tetracyclines, sulfonamides, others) may act as photosensitizing agents. The mechanism of tissue injury probably varies with the different agents.

Lesions tend to be more severe with photodynamic dermatitis than with sunburn, often resulting in exudation of serum onto the skin’s surface. Exudation is followed by drying and fissuring. The lesions are pruritic. Skin necrosis with sloughing of severely affected areas often follows. Conjunctivitis, sometimes with corneal opacity and temporary blindness, may accompany photosensitization.

Pigs with sunburn or photosensitization should be kept out of sunlight. Photosensitizing agents, once identified, should be avoided.