Epidemiological investigation of the buller steer syndrome (riding behaviour) in a western Canadian feedlot.

OBJECTIVE

To describe the buller steer syndrome in a Western Canadian feedlot.

DESIGN

a retrospective study.

ANIMALS: 78,445 male cattle that entered a 24,00-head feedlot in western Canada from 1991 to 1993.

PROCEDURE: All cattle were given a hormonal growth promotant containing 20 mg oestradiol benzoate and 20 mg progesterone within 24 h of arrival at the feedlot. A 'buller' was a steer that was observed at daily pen checking to be ridden persistently by pen mates or had evidence of having been persistently ridden by pen mates. At the completion of the feeding period, animal health records for bullers were collected and analysed.

RESULTS

The prevalence of bullers in the total population was 2,139/78,445 (2.7%, range per pen 0 to 11.2%). The prevalence of bullers increased with increasing weight and age. The relapse risk after first treatment (three days in the feedlot hospital plus treatment for concurrent disease) was 30% on average (27 to 35%). Individual records from 9,734 yearling steers that entered the feedlot in 1991 and 1992 showed that bullers were significantly (P < 0.05) heavier at processing than non-bullers. Bullers occurred as a point source epidemic with a cause occurring soon after cattle arrived at the feedlot and were mingled into pen grous. This gave a 'days on feed' distribution. 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, weather condition of 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. Reimplantation with hormonal growth promotants and castration of intact bulls did not produce an epidemic of bullers.

CONCLUSIONS

The findings of this study support the theory that bullers are the result of agonistic interactions, which occur concurrent with the establishment and maintenance of a social hierarchy with pens of feedlot cattle.