Case-control study to identify management practices associated with morbidity or mortality due to bovine anaplasmosis in Mississippi cow-calf herds

Abstract

Bovine anaplasmosis (BA) is a costly disease affecting the U.S. beef cattle industry. Chlortetracycline (CTC) in feed or mineral supplements is often used to control clinical signs of BA. The objective of this study was to determine if manage­ment practices, such as feeding CTC, are associated with ill­ness or death from BA in Mississippi cow-calf herds. Case and control herds were solicited from veterinary practices across Mississippi. Cases were herds with clinical BA diagnosed by a veterinarian within the previous calendar year. Controls were herds under the care of the same practice with no clini­cal BA diagnosed in the previous year. Blinded interviewers conducted telephone surveys of case and control herd owners. Management and biosecurity factors were tested for associa­tion with herd status using a logistic regression generalized linear mixed model with veterinary practice as a random vari­able. Twenty-two case and 25 control herds from 6 veterinary practices across Mississippi were interviewed, representing 22 counties. The average herd size was 132 for case herds, and 136 for control herds. Twenty case herds and 13 control herds fed CTC medicated mineral or feed. Providing CTC was associated with case herd status (OR = 9.2, 95% C.I. = 1.7-50.7). The association observed between case herds and feeding CTC might be because: 1) herds that had experienced previous BA morbidity and mor­tality subsequently began feeding CTC, or 2) some individual cattle consume enough CTC to achieve clearance of the per­sistent carrier state, thereby increasing risk of reinfection and clinical BA.