VIRULENCE DIFFERENCES AMONG 3 STRAINS OF HEMOPHILUS-SOMNUS FOLLOWING INTRATRACHEAL INOCULATION OF CALVES

  • 1 July 1988
    • journal article
    • research article
    • Vol. 52  (3) , 349-354
Abstract
Pneumonia was induced in four month old Holstein calves by intratracheal inoculation of 1 .times. 109 colony forming units of Haemophilus somnus. Twenty calves were divided into four groups of five and challenged with a pneumonic strain (Group 1), an encephalitic strain (Group 2), a preputial strain (Group 3), or a placebo (Group 4). The clinical score, neutrophil count, respiratory rate, and temperature were significantly increased in group 1 by day 1 postinoculation(P < 0.05) and maintained until day 6 postinoculation (P < 0.05). The macroscopic pathological changes were significantly greater in group 1 (P < 0.05). Haemophilus somnus were consistently isolated from pneumonic tissue of group 1 only. Groups 2 and 3 had mild transient increases in all parameters measured and macroscopically only small focal lesions were present. It is concluded that virulence differences exist between H. somnus strains following intratracheal challenge of bovine lungs.