Growth of Escherichia coli in Milk from Endotoxin-Induced Mastitic Quarters and the Course of Subsequent Experimental Escherichia coli Mastitis in the Cow

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Abstract
The objective of this study was to assess growth of Escherichia coli in milk from endotoxin-induced mastitic quarters and to relate the in vitro findings to the course of experimental E. coli mastitis. Whole and skim milks from 24 rear quarters of 12 cows were inoculated with E. coli 0:157 and incubated at 38.degree.C. Growth of E. coli 0:157 was not inhibited in milk collected from rear quarters immediately prior to endotoxin infusion. However, growth inhibition occurred in all but one whole mastitic milk samples collected from mastitic quarters 18 h after infusion of .1 mg of endotoxin. Skim milk samples from mastitic quarters were bactericidal in four cows (7 quarters), whereas growth occurred in skim mastitic milk from 17 quarters of nine cows. Rear quarters of all cows were inoculated with 104 cfu of E. coli 0:157 19 h after the quarters had been infused with endotoxin. Clinical parameters and milk production were monitored during 36 h and 21 d, respectively. None of the inoculated quarters developed signs of inflammation, and secreta from inoculated quarters were bacteriologically negative after 48 h. Therefore, growth-inhibitory property of skim milk from endotoxin-induced quarters was apparently not a suitable parameter to monitor differences in susceptibility to E. coli mastitis.