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Intramammary Challenge of the Bovine Mammary Gland with Coliform Bacteria During Early Involution

Department of Dairy Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691

Isolates of Escherichia coli (n = 12), Klebsiella pneumoniae (n = 20), and Klebsiella oxytoca (n = 10) were used to challenge involuting mammary glands at 7 d of the dry period. Bacteria were selected for challenge on the basis of their ability lo grow in a pooled source of dry cow secretion obtained at 21 d of involution. Challenge bacteria were classified as highly adapted (in vitro growth > 7 cfu log₁₀/ml) or poorly adapted (growth < 2 cfu log₁₀/mt) for growth in dry cow secretion. Intramammary infusion of Escherichia coli, K. pneumoniae, and K. oxytoca resulted in 0, 40, and 30%, respectively, of quarters infected. Isolates highly adapted for growth in dry cow secretion caused 75% of K. pneumoniae and 67% of K. oxytocaM experimental intramammary infections. Results indicated that the ability to overcome inhibitory properties of dry cow secretion was related to the establishment of K. pneumoniae and K. oxytoca intramammary infections in the dry gland. There was no evidence that growth of E. coli in dry cow secretion related to pathogenicity in the dry gland. Experimental challenge using multiple isolates did confirm the resistance of the involuting mammary gland to E. coli infection.