Quick Answer: Coccidiosis is an intestinal parasite infection that mainly strikes chicks between 2 and 8 weeks old, causing bloody or dark diarrhea, pale combs, lethargy, and reduced appetite. The standard treatment is Corid (9.6% amprolium) mixed into the flock’s only water source — 1 teaspoon per gallon for a moderate outbreak or 2 teaspoons per gallon for a severe one, per Chicken Fans — given for 5-7 days, with most birds improving within 24 hours. Amprolium has a zero-day egg withdrawal, so eggs stay safe to eat during treatment, and medicated starter feed or hatchery vaccination prevents most cases before they start.
Coccidiosis is the leading cause of death in young chicks, and it moves fast once it takes hold — a bird that looked fine the day before can be huddled, off its feed, and passing bloody droppings within 24-48 hours. It’s caused by Eimeria, a protozoan parasite that damages the intestinal lining as it multiplies, and damp, contaminated bedding is what lets it spread through a flock. This guide covers how to recognize it early, the correct Corid dosage for moderate versus severe outbreaks, and how medicated feed or vaccination heads it off before it starts.
Symptoms by severity
| Sign | Early/mild | Moderate | Severe |
|---|---|---|---|
| Droppings | Slightly loose | Dark, tarry diarrhea | Visible blood, watery |
| Appetite | Slightly reduced | Off feed, huddling | Not eating or drinking |
| Comb/wattles | Normal color | Pale | Pale, ruffled, hunched |
| Corid dose | Prevention: 1/2 tsp/gal | 1 tsp/gal (0.012%) | 2 tsp/gal (0.024%) |
By the numbers
- Backyard chicks are most susceptible to coccidiosis between 2 and 8 weeks old, the window before their natural immunity develops, per Freedom Ranger Hatchery.
- The moderate-outbreak Corid dose is 1 teaspoon of 9.6% liquid per gallon of water (0.012%); a severe outbreak with visible blood steps up to 2 teaspoons per gallon (0.024%), given for 5-7 days as the flock’s only water source, per Chicken Fans.
- Amprolium carries a zero-day egg and meat withdrawal period under its FDA approval for laying hens, so eggs collected mid-treatment remain safe to eat, per Kent Nutrition.
1. Catch it early — watch droppings and comb color
Check droppings and combs daily during brooding
- Lethargy, huddling near the heat source, and reduced feed intake often show up a day or two before droppings visibly change.
- Pale combs and wattles signal blood loss from intestinal damage — a red flag that treatment shouldn't wait.
- A quick daily glance at the brooder floor catches an outbreak while it's still one or two birds instead of the whole batch.
Ordering chicks in bulk from a hatchery for the first time, or adding several new birds to an existing flock, is exactly when a fast, reliable water treatment on hand matters most. Try Prime free for 30 days and next-day delivery on Corid or a backup electrolyte pack means you’re not waiting two or three days once symptoms show up.
2. Treat with Corid at the right dose
Corid 9.6% Oral Solution (amprolium)
- Mix a fresh batch daily and make Corid water the flock's only source — no separate plain-water waterer during treatment, or birds will just drink around the dose.
- Don't add vitamins or other medications to the same water; some interfere with how amprolium works against the parasite.
- Most sick birds show visible improvement within 24 hours, but complete the full 5-7 days even if symptoms clear early to prevent a rebound.
3. Treat the whole flock, not just the sick birds
Coccidia spreads through droppings-contaminated bedding, feed, and water, so by the time one bird shows symptoms, the rest of the flock has almost certainly been exposed too. Dosing only the visibly sick birds leaves the parasite circulating in birds that look fine but are still shedding oocysts, which is how outbreaks come back within a week or two of an apparently successful treatment. Our chicken electrolytes guide covers the supplements worth having ready for the recovery window right after a Corid course finishes.
4. Prevent it with medicated feed or vaccination — never both
| Approach | How it works | Key rule |
|---|---|---|
| Medicated starter feed | Low preventative dose of amprolium builds tolerance as chicks develop immunity | Never combine with a coccidiosis-vaccinated chick |
| Hatchery vaccination | Live, weakened oocysts given at hatch train natural immunity | Medicated feed afterward kills the live vaccine |
Medicated chick starter feed (amprolium)
- Ask the hatchery or feed store whether your chicks were vaccinated for coccidiosis before choosing medicated or non-medicated starter.
- Keep chicks on starter/grower feed until they're about to lay, then transition to layer feed — see our chicken feed guide for picks of both types.
- Damp, muddy bedding is the main risk factor since oocysts thrive in wet conditions — a dry run with a roof, covered in our chicken run guide, cuts exposure significantly.
The bottom line
Watch droppings and comb color daily during brooding — dark, tarry, or blood-streaked droppings alongside a pale, lethargic bird means coccidiosis, not a passing upset stomach. Corid (9.6% amprolium) at 1 teaspoon per gallon for moderate cases or 2 teaspoons per gallon for severe ones, given as the flock’s only water for 5-7 days, is the standard treatment and works fast — most birds improve within a day. Long-term, medicated starter feed or hatchery vaccination (never both together) and a dry, well-drained run prevent the large majority of outbreaks from starting at all.