Coccidiosis, caused by protozoan parasites of the genus Eimeria, is one of the most economically significant and welfare-impactful diseases in commercial poultry production.
Subclinical coccidiosis - infection without obvious clinical signs - may be the most significant welfare concern at population level because it affects millions of chickens simultaneously while remaining below the threshold of obvious suffering that triggers intervention. Affected birds experience intestinal damage, nutrient malabsorption, immune activation, and chronic low-level discomfort. Clinical outbreaks cause acute suffering including bloody diarrhea, weakness, and high mortality. Intensive housing conditions accelerate disease spread, creating a cycle where the productivity-focused housing system itself drives welfare problems.