Diseases and pathogens associated with mortality in Ontario beef feedlots

Area of Science:

• Veterinary Pathology
• Bovine Medicine
• Animal Health Economics

Background:

• Early mortality in beef feedlot calves significantly impacts economic viability.
• Understanding prevalent diseases in newly arrived calves is crucial for effective herd management.
• Mycoplasma bovis has been increasingly implicated in calfhood morbidity and mortality.

Purpose of the Study:

• To determine the prevalence of diseases and pathogens causing mortality in Ontario beef feedlot calves within 60 days post-arrival.
• To identify the primary causes of death and severe morbidity in this high-risk population.
• To assess the contribution of specific viral and bacterial agents to calf losses.

Main Methods:

• Post-mortem examinations and microbiological cultures were performed on 99 deceased or euthanized calves.
• Immunohistochemical staining was utilized for Bovine Viral Diarrhea Virus (BVDV) antigen detection.
• Data from 72 Ontario beef feedlots were analyzed to determine disease prevalence.

Main Results:

• Pneumonia was the most frequent cause of mortality (69%), with both fibrinosuppurative and Mycoplasma bovis-associated caseonecrotic bronchopneumonia being highly prevalent.
• Mycoplasma bovis was the most common bacterial isolate from lungs (82%) and was associated with pneumonia and/or arthritis in 36% of cases.
• Bovine Viral Diarrhea Virus (BVDV) was detected in 35% of cases, contributing to viral respiratory disease and other BVDV-related conditions.

Conclusions:

• Pneumonia, especially Mycoplasma bovis-associated pneumonia and polyarthritis, is a major driver of mortality in Ontario beef feedlot calves.
• Effective management strategies targeting both bacterial (M. bovis) and viral (BVDV) pathogens are essential for reducing early calf losses.
• The study underscores the emerging significance of Mycoplasma bovis in feedlot calf health.