EPIDEMIOLOGIC INVESTIGATION OF THE BULLER STEER SYNDROME (RIDING BEHAVIOR) IN A WESTERN CANADIAN FEEDLOT

Objective To describe the buller steer syndrome in a Western Canadian feedlot.Design retrospective epidemiological study. Animals 78,445 mal e cattle that entered a 24,000-head feedlot in western Canada from 199 1 to 1993. Procedure All cattle were given a hormonal growth promotant containing 20 mg oestradiol benzoate and 200 mg progesterone within 2 4 h of arrival at the feedlot. A 'buller' was a steer that was observe d at daily pen checking to be ridden persistently by pen mates or had evidence of having been persistently ridden by pen mates. At the compl etion of the feeding period, animal health records for bullers were co llected and analysed. Results The prevalence of bullers in the total p opulation was 2139/78,445 (2.7%, range per pen 0 to 11.2%). The preval ence of bullers increased with increasing weight and age. The relapse risk after first treatment (three days in the feedlot hospital plus tr eatment for concurrent disease) was 30% on average (27 to 35%). Indivi dual records from 9734 yearling steers that entered the feedlot in 199 1 and 1992 showed that bullers were significantly (P < 0.05) heavier a t processing than non-bullers. Bullers occurred as a point source epid emic with the cause occurring soon after cattle arrived at the feedlot and were mingled into pen groups. This gave a 'days on feed' distribu tion. The peak incidence of bullers occurred much sooner after arrival and dropped off much quicker in older cattle. The daily incidence of bullers was temporal, but was not related to season of the year, weath er conditions or any other feedlot management practice. It was related to the seasonal arrival of cattle at the feedlot, their age at entry to the feedlot and the post arrival occurrence of bullers. Reimplantat ion with hormonal growth promotants and castration of intact bulls did not produce an epidemic of bullers. Conclusion The findings of this s tudy support the theory that bullers are the result of agonistic inter actions, which occur concurrent with the establishment and maintenance of a social hierarchy within pens of feedlot cattle.