Coccidiosis in Chickens: Symptoms, Causes and Treatment

Coccidiosis is caused by Eimeria protozoa - there are 9 species that infect chickens, each targeting a specific region of the intestine. The most pathogenic species are E. tenella (cecal - causes cecal bleeding and the classic bloody droppings), E. necatrix, and E. brunetti.

Cocci oocysts are shed in feces and become infective in the environment within days. Chicks are infected by ingesting oocysts from contaminated soil, litter, feed, or water. The parasite then destroys intestinal cells during replication - the bleeding and diarrhea are from this cellular destruction, not from the parasite itself.

Why it hits chicks hardest (3-6 weeks):

• No acquired immunity yet - adult birds build immunity through low-level exposure
• Young intestinal tissue is more vulnerable to cellular destruction
• Higher fecal-oral contact in brooder environments
• Stress of weaning and temperature transitions coincides with peak vulnerability

Triggers for outbreak in older birds:

• Introduction of new birds from a different environment (carrying different Eimeria strains)
• Immunosuppression from Marek's disease, IBD, or other illness
• Heavy rain flooding the coop and concentrating oocysts
• Overcrowding increasing fecal contamination density

Presumptive diagnosis is based on clinical signs - bloody droppings in chicks 3-6 weeks old is coccidiosis until proven otherwise. Confirmatory diagnosis requires a fecal float to identify Eimeria oocysts under microscopy.

Important distinction: Cecal droppings (normal) are brown and foamy, sometimes with a slight orange tinge. Coccidial bloody droppings are frank red blood, often with mucus. If you're uncertain, treat - the cost of treating unnecessarily is low; the cost of not treating is high.

Post-mortem findings (if a chick dies):

• E. tenella: Swollen, blood-filled ceca with visible petechiae (small hemorrhages)
• E. necatrix: Small intestine thickened, fluid-filled, with white spots (oocyst clusters)
• E. brunetti: Lower small intestine and colon lesions

Amprolium (Corid) - first-line treatment

Amprolium is a thiamine antagonist that starves the parasite of the B-vitamin it needs to reproduce. It is available OTC, has no egg withdrawal requirement, and is highly effective.

• High-dose treatment (active outbreak): 1.5 teaspoons of Corid 20% soluble powder (or 2 teaspoons liquid Corid 9.6%) per gallon of water for 5-7 days
• Prevention dose: 1/3 teaspoon Corid 20% per gallon for 21 days in high-risk situations
• Make fresh solution every 24 hours
• Remove all other water sources - treated water must be their only water source
• Supplement with B vitamins after treatment (Amprolium blocks thiamine absorption - give a B-complex for 3-5 days after completing treatment)

Sulfonamides (alternative): Sulfadimethoxine (Albon) is effective but requires vet prescription and has longer egg/meat withdrawal times.

Supportive care alongside medication:

• Electrolytes in water (Sav-A-Chick or similar)
• Vitamin K supplementation - cocci destroys the intestinal cells responsible for vitamin K synthesis, leading to clotting failure
• Keep chicks warm - sick chicks lose thermoregulation
• Isolate severely affected birds from healthy flock members

Amprolium dosing for coccidiosis in chickens

Amprolium is sold over the counter as Corid at farm and livestock supply stores. For the common 9.6% liquid, mix 2 teaspoons per gallon of drinking water; for 20% soluble powder, mix 1.5 teaspoons per gallon. Provide it as the only water source for 5-7 days and mix fresh solution daily. Amprolium has a zero-day egg withdrawal under its labeled poultry use, but keepers should verify the current product label and local veterinary guidance.

• Controlled exposure in chicks - allow small amounts of soil and outdoor exposure from week 2 onward, so chicks build immunity gradually before oocyst load overwhelms them
• Never use medicated chick starter with vaccinated chicks - Amprolium interferes with the coccidiosis vaccine
• Keep brooder dry - wet litter concentrates oocysts and dramatically increases infection pressure
• Clean waterers daily - oocysts accumulate in waterer residue
• Fermented feed 3-4x per week reduces oocyst shedding and builds gut immunity
• Oregano and thyme in water 3x per week (coccidiostatic)
• Do not move chicks to the adult coop too early - let immunity develop first (typically 8-10 weeks)