Physical characteristics of the bovine teat canal and their influence on susceptibility to streptococcal infection.

Physical characteristics of the bovine teat canal were examined for their influence on susceptibility to intramammary infection. All quarters of 18 cows were inoculated with 2 x 10(5) cfu Streptococcus agalactiae (Trial 1) and 20 cows with 10(5) cfu Str. uberis (Trial 2) 3-4 mm into the teat canal every 3 d for 12 d. Incidence of quarter infection was similar for both pathogens, 30/72 (42%) in Trial 1 and 32/80 (40%) in Trial 2. Logistic regression analysis showed that probability of infection by Str. agalactiae increased significantly with an increase in quarter peak flow rate (P < 0.05) whereas probability of infection increased for Str. uberis with a decrease in teat canal length (P < 0.05). A significantly higher (P < 0.001) incidence of infection by Str. uberis was observed in quarters that contained a low wet weight (< 1.8 mg) of removable keratin compared with those that contained > 1.8 mg keratin, but there was no correlation between weight of keratin and length of the teat canal. Infections by Str. uberis took significantly less (P < 0.05) time to show a rise in somatic cell count above 7.5 x 10(5) cells/ml than Str. agalactiae. The results provide evidence that these pathogens use different mechanisms to pass through the teat canal.