Causes of Mortality in Backyard Poultry in Eight States in the United States

Poultry Health & Disease
Written By Jennifer Bryant

Research Review

What do backyard poultry actually die from when owners submit them to veterinary diagnostic laboratories? This multi-state study found that deaths were often complicated rather than caused by one isolated problem. Tumor-forming diseases, bacteria, parasites, viruses, toxins, poor condition, and management-related stressors frequently overlapped in the same bird.

Source Paper

Cadmus, K. J., Mete, A., Harris, M., Anderson, D., Davison, S., Sato, Y., Helm, J., Boger, L., Odani, J., Ficken, M. D., & Pabilonia, K. L. (2019). “Causes of mortality in backyard poultry in eight states in the United States.” Journal of Veterinary Diagnostic Investigation, 31(3), 318–326. Read the peer-reviewed open-access paper: https://doi.org/10.1177/1040638719848718

Why This Paper Matters

When a backyard bird dies, it is tempting to choose the most obvious symptom and assign one cause. This paper shows why that approach can fail. Many birds had a primary diagnosis plus parasites, bacteria, poor body condition, toxins, or another condition that increased the total disease burden.

Study at a Glance

  • Species: Mostly chickens, with some turkeys, ducks, and geese

  • Birds: 2,687 birds represented in 2,509 diagnostic reports

  • Study period: 2015–2017

  • Locations: Veterinary diagnostic laboratories in eight U.S. states

  • Journal and year: Journal of Veterinary Diagnostic Investigation, 2019

  • Focus: Infectious disease, noninfectious disease, neoplasia, parasites, toxins, and public-health risks

How the Study Was Conducted

Researchers reviewed backyard-poultry necropsy reports from diagnostic laboratories in California, Colorado, Georgia, Hawaii, Iowa, Pennsylvania, South Carolina, and Texas. They classified the primary cause of mortality and recorded significant contributing diagnoses. The dataset included birds that were sick or dead enough to be submitted for testing; it was not a random survey of every backyard flock.

Key Findings

  • Neoplasia and lymphoproliferative disease were the most common primary category, involving 42.1% of submitted birds.

  • Marek’s disease and leukosis or sarcoma-type diseases made up many tumor-related diagnoses.

  • Bacterial organisms were detected in 42% of birds, parasites in 28%, and viruses in 7%; these groups overlap because birds often had multiple findings.

  • A total of 69.1% of birds had more than one possible disease or contributing problem.

  • Zoonotic organisms included paratyphoid salmonellae, Campylobacter species, Listeria monocytogenes, and Mycobacterium avium.

  • Lead and other heavy metals were identified in some birds, raising concerns for both flock health and household food safety.

What the Numbers Do—and Do Not—Mean

These percentages describe problem cases submitted to diagnostic laboratories. They do not represent the prevalence of disease in all backyard flocks. Owners are more likely to submit sudden, unusual, severe, or unexplained deaths, so sick birds are deliberately overrepresented. Testing also differed by laboratory and by what owners authorized or could afford.

Why Necropsy Matters

Several important conditions cannot be separated reliably by outward symptoms alone. Necropsy, histopathology, culture, PCR, toxicology, and parasite testing can reveal a primary disease and the additional burdens surrounding it. One dead bird can provide information that protects the rest of the flock when the cause is investigated promptly.

Practical Prevention Lessons

  • Quarantine new birds before they enter the resident flock.

  • Reduce contact with wild birds and rodents.

  • Keep feed and water clean and protect them from fecal contamination.

  • Avoid overcrowding and chronic environmental stress.

  • Use a planned parasite-monitoring and control strategy.

  • Prevent access to peeling paint, contaminated soil, hardware, and other sources of lead or heavy metals.

  • Vaccinate where appropriate, legally available, and compatible with the flock’s risk profile.

  • Use veterinary diagnostics for unexpected deaths instead of treating the entire flock from a guess.

Strengths of the Study

The study combined real veterinary diagnostic data from eight states and thousands of birds. It did not depend on owners identifying disease from symptoms. The detailed necropsy and laboratory findings also allowed researchers to capture multiple simultaneous conditions rather than forcing every bird into one oversimplified explanation.

Limitations of the Study

Submission bias is the largest limitation: these birds were already sick, dead, unusual, or concerning enough to reach a diagnostic laboratory. Testing practices varied among states and cases. The study is valuable for understanding what laboratories find in mortality cases, but it should not be used to diagnose a living bird or estimate the risk to every flock.

Poultry Nerds Takeaway

Backyard poultry deaths are frequently layered. Prevention works best as a system—biosecurity, clean housing, sensible stocking density, parasite management, vaccination when appropriate, toxin prevention, and diagnostics when something goes wrong. When deaths are sudden, multiple birds are affected, or a reportable or zoonotic disease is possible, contact a poultry veterinarian, state diagnostic laboratory, extension office, or animal-health authority.

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Research Review Notice

This article summarizes a peer-reviewed scientific publication and explains its practical application for poultry keepers, breeders, and educators. It is an original Poultry Nerds review, not a reproduction of the manuscript. It is educational and is not a diagnosis or treatment plan. Work with a veterinarian or diagnostic laboratory for sick birds, unexpected deaths, suspected zoonotic disease, or a possible reportable disease.

Jennifer Bryant
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