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1 Milk Secretion and Mastitis Laboratory, Livestock and Poultry Science Institute, US Department of Agriculture, ARS, Beltsville, MD 20705, Animal Health Laboratory, University of Vermont, South Burlington 05403
2 Milk Secretion and Mastitis Laboratory, Livestock and Poultry Science Institute, US Department of Agriculture, ARS, Beltsville, MD 20705, Animal Health Laboratory University of Vermont, South Burlington 05403
Influence of teat canal keratin on susceptibility to intramammary infection was investigated in lactating Jersey cows. In each of two replicate trials, keratin was removed from the left teats of 20 cows immediately before milking. Immediately after milking, all teats were exposed to bacterial challenge by immersion in a suspension of Streptococcus agalactiae (5 x 107 cfu/ml). Bacterial challenge was repeated after the next four milkings. Foremilk samples were obtained for 8 d after keratin removal to determine infection status. A mammary quarter was classified as infected based solely upon the bacteriological criteria outlined by the National Mastitis Council. The rate of infection in quarters from which keratin was removed was greater than that in control quarters. Infection rates were 26.3% for keratin-removed quarters and 8.3% for control quarters in trial 1 and 13.5 and 0%, respectively, in trial 2. When more stringent criteria (recovery of >l00 cfu of S. agalactiaelml in three or more successive milk samples and a SCC of >l06) were used to identify a subset of infections that were clearly intramammary, infection rates were 9.3% for keratin-removed quarters and 1.4% for control quarters. Thus, partial removal of keratin from the teat canal compromised the ability of the teat to prevent passage of bacterial pathogens from the external environment into the mammary gland.
Key Words: keratin • mastitis • teat
Submitted on December 23, 1991
Accepted on April 13, 1992
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