Nine of 250 cows on a dairy farm initially developed severe dermatitis on parts of their bodies that touched the floor, and it then spread over their entire body. The cause was suspected to be calcium cyanamide, which had been added to the material spread on the floor to prevent environmental mastitis. Experimental exposure of the skin of a cow to calcium cyanamide induced the same type of contact dermatitis, and histopathological investigations showed that it caused irritant and allergic reactions. To identify the cause of the dermatitis, a patch test with calcium cyanamide and its breakdown products, cyanamide, urea and ammonium bicarbonate, was carried out on four cows. Three of them had a positive reaction to calcium cyanamide and cyanamide; delayed and amplified reactions suggesting an allergic response were observed.
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