EFFICACY OF IMMUNIZATION OF FEEDLOT CALVES WITH A COMMERCIAL HEMOPHILUS-SOMNUS BACTERIN

  • 1 April 1988
    • journal article
    • research article
    • Vol. 52  (2) , 191-198
Abstract
Two cohorts, consisting of 10,723 calves total, were identified in the prospective follow-up study to investigate whether immunization of auction market beef calves immediately upon arrival at the feedlot with a commercial Haemophilus somnus whole cell killed bacterin would reduce subsequent mortality. In addition to mortality rate, the use of incidence rate of fatal disease is introduced as an effect measure to examine vaccine efficacy in the feedlot. The Haemophilus somnus bacterin had no significant effect on the overall crude mortality rate; however, the bacterin appeared to significantly (p < 0.05) reduce the incidence rate of fatal disease and the mortality rate during the first two months in the feedlot, when risk of fatal disease onset was highest. Once mortalities likely not associated with hemophilosis (for example, a fractured femoral neck) were removed from the analysis, steer mortality rate, but not heifer mortality rate, was reduced significantly (p < 0.05) in the vaccinated group. The attributable percent overall for steers was 17.4%; this suggests that 17.4% of fatal respiratory disease in the unvaccinated steers could have been prevented by vaccination with the H. somnus bacterin. Heifer calves demonstrated a significantly (p < 0.01) higher incidence rate of fatal disease during the first week than did steer calvers, indicating that a different pattern of fatal disease existed for the two sexes. Use of a second vaccination two weeks after arrival did little to decrease mortality risk.