PRIMARY PHOTOSENSITIZATION RELATED TO INGESTION OF ALFALFA SILAGE BY CATTLE

A herd of 650 Holstein cows was examined for skin disease. Approximate ly 400 of the lactating adults were affected, but heifers, calves, and nonlactating cows were clinically normal. The condition was character istic of primary photosensitization. Milk production; of the affected cows was normal. Affected cows did not appear to be ill, and none of t he cows was icteric. Three of 7 cows had high serum gamma-glutamyltran sferase activities, but in the other 4 cows, activity was within the r eference range. Serum activities of other hepatic enzymes were within reference ranges in the 7 cows that were examined. Hepatic biopsy spec imens from 3 cows were normal. Specimens from 4 other cows had changes that ranged from minimal to mild, chronic, lymphoplasmacytic periport al hepatitis to acute, random, necrotizing hepatitis. Development of p hotosensitivity was related to ingestion oi alfalfa silage. Acetone ex tracts of the alfalfa silage, but not of other feedstuffs, were found to inhibit growth of Candida albicans under ultraviolet light. Cows ex perimentally fed a diet composed exclusively of the alfalfa silage dev eloped skin lesions after 6 days, but did not have detectable serum co ncentrations of phylloerithrin.