Coccidiosis: the silent FCR killer
Mortality is usually low. The loss is in feed conversion, in uniformity, and in the gut damage that opens the door to necrotic enteritis.
Awaiting veterinary review. This guide is written from published industry practice and has not yet been checked by our domain advisor. Confirm anything clinical with your own veterinarian before acting on it.
Coccidiosis is caused by Eimeria, a protozoal parasite that lives in the gut wall. It is present on essentially every poultry farm, and the question is never whether you have it — only whether it is costing you enough to notice.
The subclinical case is the expensive one
Acute coccidiosis is visible: blood in droppings, huddled birds, mortality. Most farms recognise it.
Subclinical coccidiosis produces none of that. The parasite damages the lining of the gut, absorption falls, and the bird eats the same feed while extracting less from it. What you see is:
- FCRFeed conversion ratio — kilograms of feed to put on a kilogram of live weight. The single most useful number in broiler production, because feed is 60–75% of what the bird cost.Glossary → drifting upward
- Growth falling behind target
- Poor flock uniformity
- Mortality · deathsامواتamwaatThe daily number every farmer tracks, even on paper.Glossary → that looks completely normal
This is the classic explanation when FCR worsens and nothing in the shed looks wrong. If management is sound and conversion is still drifting, gut health is where to look.
Why it is always there
Eimeria oocysts are shed in droppings, survive in litter, and become infective after a day or two in warm, damp conditions. A bird pecking at litter is constantly re-exposing itself.
That is also why litter management is a coccidiosis control measure, not just a comfort one. Wet patches under drinkers are where oocysts sporulate best.
What to look at
Birds aged roughly three to six weeks are the usual window. Worth checking:
- Droppings. Blood is obvious; orange, mucoid or loose droppings are the subtler sign.
- Litter condition. Wet, capped litter both causes and signals a problem.
- Uniformity. A widening spread in bird weights is often gut health.
Confirming it is a vet’s job — the species of Eimeria involved affects which part of the gut is damaged and what treatment makes sense.
Prevention and treatment
In-feed prevention. Most commercial broiler rations already contain an ionophore coccidiostat. Ask your mill what is in the feed before adding anything in water — doubling up risks overdose, and ionophores are toxic to some other species.
Water treatment. Amprolium and toltrazuril are the common treatments. Amprolium works by blocking thiamine uptake in the parasite, which means prolonged use can induce thiamine deficiency in the birds.
No dosages here, deliberately. Dose depends on the product, the concentration and the bird. The label and your vet govern.
The resistance problem
Eimeria develops resistance to anticoccidials, which is why programmes rotate products between cycles rather than running one indefinitely. If a product that used to work stops working, resistance is a likelier explanation than a bad batch.
The cheapest control
Dry litter, working drinkers, and not overstocking. None of it costs anything, and all three reduce the oocyst load a bird is exposed to more reliably than any product in a bottle.