VARIATION OF ABSCESS FORMATION IN CATTLE AFTER VACCINATION WITH A MODIFIED-LIVE PASTEURELLA-HAEMOLYTICA VACCINE

During the spring of the first year of a vaccine study, 57 of 238 calv es (24%), in which modified-live Pasteurella haemolytica vaccine (MLV) was injected twice, developed 1 or more abscesses. Abscesses were not observed after multiple visual examinations of 437 calves given kille d P haemolytica bacterin or placebo injections of similar adjuvants us ed in the vaccine and bacterin. Calves that developed abscesses after the second injection of MLV weighed significantly (P < 0.05) less (on the basis of body weight adjusted for weaning weight) at the second in jection than did those that did not develop abscesses. Compared with c alves given MLV that did not develop observable abscesses, calves deve loping abscesses after the second injection of MLV weighed 11.0 and 14 .2 kg less, respectively, at 56 days and 112 days after injection, and they had 11.0 kg less gain at 56 days after injection. Abscess preval ence tended to be highest on certain days or at certain locations used for cattle processing, and the prevalence of abscesses increased in c attle processed later on a given day. Abscesses were not observed in 2 other groups of similarly treated calves vaccinated in the autumn or in the subsequent spring.