Baxter Black: Photosensitization
July 13, 2017
Like a good boy I subscribed my mother to one of the papers that carries my column. Later I asked her how she liked it. She said, "It's fine, son. I like most of 'em but those where you ramble on about cow diseases and stuff like that I really don't find near as interesting."
Well, bear with me, Mom, here goes another. Summertime brings with it bathing suit ads, lawn mower commercials, kids home to help with the chores, mosquitos, firecrackers and PHOTOSENSITIZATION. Photo: light; sensitization; sensitive to. Sensitive to sunlight. And that is an understatement! We're talkin' hard core, fourth and goal, damn the torpedo's, all ahead full sunburn! Not to be confused with true sunburn or snowburn.
The animal is sensitized to the sun's rays so that even a lot of the weaker rays can cause damage. An animal cannot be sunburned through a window glass but can be photosensitized through it.
It occurs in sheep, grazing cattle and I've seen it show up in the feedyard. Most commonly is related to the ingestion of specific plants the animal has eaten. St John's wort (Klamath weed) in the Northwest, agave and sachuiste in the Southwest, plus others including cultivated rape, horse brush and buckwheat. Sudan grass, clover or alfalfa have even been incriminated.
Either through liver damage or directly, breakdown products of the plant enter the blood stream and circulate to the skin. There they become exposed to the sun's penetrating rays. A chemical reaction occurs which damages the surrounding capillaries and tissue. Thick hair or darkly pigmented skin usually blocks out the sun's rays so the reaction only occurs in the lighter areas.
Following ingestion of enough plant toxins the affected critter's skin begins to redden, itch and swell. By the second day the muzzle and eyelids have a burned appearance. With continued exposure to sunlight the skin dies, becomes hard and leathery and starts to peel at the edges of the eyes or muzzle.
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Looking at an animal in this condition can often be confusing until you feel the white parts of his skin. On a Hereford, the red-pigmented skin will be normal but as soon as you touch the border where the white begins, it feels like dry rawhide. It occurs in whiteface sheep, Herefords, Charolais, Holsteins, and anything with non-pigmented white skin.
Supportive medicine to prevent infection and reduce inflammation may help out but SHADE is the only long-term treatment. They usually survive but the affected skin may peel plumb off.
I've even taken the ol' blue lotion and painted a few. I did that to a Hereford steer one time and put a white paper star on his head. He looked like an American flag comin' down the alley!
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