Experimentally Induced Coliform (Aerobacter aerogenes) Mastitis in Normal Cows and in Cows Made Neutropenic by an Equine Anti-Bovine Leukocyte Serum

Abstract

SUMMARY Three cows having normal peripheral blood neutrophil counts developed acute mastitis within 4 to 6 hours after they were given 0.65 to 1.7 million viable Aerobacter aerogenes in a normal lactating quarter. The resulting leukocytosis into the milk immediately restricted bacterial multiplication. Swelling and firmness of the gland subsided in 24 to 36 hours, A. aerogenes disappeared from the glands after 7 to 9 days, and leukocytosis into the milk gradually subsided; normal milk returned within 2 weeks. Two cows were made neutropenic with an equine anti-bovine leukocyte serum ( eabls ) and were exposed to viable A. aerogenes in doses similar to those given the control cows. These cows developed only slight swelling and little leukocytosis into the milk during the 1st day. In the absence of significant leukocyte diapedesis into the milk, A. aerogenes increased to billions per milliliter of milk between the 10th and 30th postinoculation hours. Massive amounts of endotoxin so generated resulted in extreme inflammatory reaction, developing after 24 to 30 hours, which led to necrosis and irreversible damage to the mammary parenchyma and cessation of milk secretion by all quarters. These results indicated and further substantiated the major role that neutrophil leukocytes have in the mammary gland in defense against virulent coliform organisms whether susceptible or resistant to humoral inhibition. Furthermore, increased vascular permeability of the udder, the initial stage of a developing inflammatory reaction, seemed to be mediated largely by a system dependent on neutrophil leukocyte participation. The delayed inflammatory reaction in the neutropenic cows seemed to be initiated in the beginning stages by a system working independently of the neutrophil leukocyte.