Broiler Mortality: Welfare Implications
Mortality in broiler flocks is both a welfare indicator and a welfare cause — birds that die have typically experienced suffering before death, and mortality rates reflect the cumulative welfare status of the flock. Managing and reducing mortality is therefore a core welfare objective.
Causes of Broiler Mortality
Sudden death syndrome (SDS / "flip-over"): Acute cardiac arrest in apparently healthy, fast-growing birds. Birds are found on their backs, often the largest, best-performing individuals. Caused by cardiac arrhythmia associated with the high metabolic demands of rapid growth. A direct welfare consequence of selection for fast growth rate.
Ascites (pulmonary hypertension syndrome): Fluid accumulation in the body cavity resulting from right heart failure under the circulatory demands of rapid growth and oxygen demand. Affected birds show distended abdomens, laboured breathing, and reduced activity. Mortality may be preceded by extended period of discomfort and respiratory compromise.
Skeletal disease: Leg problems including tibial dyschondroplasia, valgus/varus deformities, and spondylolisthesis (kinky back) cause mobility impairment and chronic pain. Severely lame birds may be unable to reach food and water, compounding welfare problems before death.
Infectious disease: Respiratory, enteric, and systemic infections cause mortality following periods of clinical illness. Disease management through vaccination, biosecurity, and rapid response reduces both morbidity and mortality.
Welfare Significance of Mortality
Each death in a broiler flock typically follows a period of welfare compromise. Even apparently sudden deaths (SDS) may be preceded by subclinical cardiac dysfunction. Reducing mortality necessarily reduces welfare burden across the flock. Slaughterhouse mortality data (dead-on-arrival and condemned birds) complements on-farm mortality records in assessing total welfare burden.
Monitoring and Targets
Daily mortality records, with investigation of any deviation from expected patterns, enable early disease detection and management response. Industry targets vary by production system and breed, but cumulative mortality above 3-4% typically indicates welfare problems requiring investigation. Welfare-focused production standards set lower targets and include mortality as a key performance indicator.
Slow-Growth Breeds and Mortality
Slower-growing breeds (45-day programmes, RSPCA Assured standards) have substantially lower mortality rates from cardiac and skeletal causes, reflecting reduced metabolic stress from less extreme growth rates. Welfare improvements from breed change include both direct mortality reduction and reduced chronic disease burden in surviving birds.