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Health note: This guide is general information, not veterinary advice, and our writers are not veterinarians. If a bird is sick, injured or not improving, contact a poultry vet, and always follow product labels and your vet's instructions for any medication. How we write health content.
Medicated chick starter protects young chicks against coccidiosis, a common and often deadly intestinal parasite disease. In the US it contains a coccidiostat, usually amprolium, which holds the parasites back while chicks build their own immunity. It does not contain antibiotics. Feed it to unvaccinated chicks, not to chicks vaccinated for coccidiosis, and don’t rely on it to stop an outbreak that has already started.
Key Takeaways
- Medicated starter contains a coccidiostat (usually amprolium) to help prevent coccidiosis in young chicks.
- Amprolium is not classed as an antibiotic. Medically important antibiotics in feed have required a vet’s Veterinary Feed Directive since 2017.
- Don’t feed medicated starter to chicks vaccinated for coccidiosis: it can stop the vaccine from working.
- Most chickens develop natural immunity by 8 to 12 weeks with light exposure; many keepers feed medicated starter for that period.
- An active outbreak is treated with amprolium in the drinking water, not with medicated feed.
Correction: an earlier version of this article said medicated starter contains antibiotics and protects against bacterial infections, gave an incorrect salinomycin level, recommended medicated feed for outbreaks and included statistics we could not verify. These have been corrected or removed.
What Is in Medicated Chick Feed?
Medicated chick starter is an ordinary starter feed with a coccidiostat added. In backyard feeds the coccidiostat is usually amprolium. Amprolium blocks thiamine (vitamin B1), which fast-multiplying coccidia need in large amounts, so it limits the parasites without stopping chicks from being exposed to them. That light exposure is how chicks develop their own immunity. Federal feed rules list amprolium in feed for replacement chickens “for development of active immunity to coccidiosis”.
Some commercial feeds use other coccidiostats, such as the ionophore salinomycin (approved at 40 to 60 g per ton). Salinomycin is not approved for laying hens, and it can be fatal if horses or adult turkeys eat it. Always check the medication and warnings on the feed tag.
Does Medicated Feed Contain Antibiotics?
Not in the usual US chick starter. Amprolium is a coccidiostat and is not classed as an antibiotic. Since January 2017, medically important antibiotics can only be added to animal feed under a veterinarian’s Veterinary Feed Directive, and not for growth promotion. So the medicated starter you buy off the shelf at a farm store is not an antibiotic feed.
Which Chicks Should Eat Medicated Starter?
| Chicks | Medicated starter? | Why |
|---|---|---|
| Not vaccinated for coccidiosis | Yes, recommended | Helps protect them while they build immunity, usually for the first 8 to 12 weeks |
| Vaccinated for coccidiosis at the hatchery | No | The vaccine relies on live coccidia multiplying in the gut; a coccidiostat can stop it working |
| Unsure whether vaccinated | Ask the hatchery or seller | The order or box label usually says if chicks were vaccinated |
Check the tag of a medicated feed for the drug and level, and follow its directions.
Can Laying Hens Eat Medicated Feed?
Federal rules do allow amprolium in feed for laying chickens, with no withdrawal period listed, so eggs from hens that eat amprolium feed at the approved level don’t need to be thrown away. But chick starter is formulated for growing chicks, not for laying hens, which need a layer feed with more calcium. Switch to a grower and then a layer feed as the birds mature. Feeds containing other coccidiostats, such as salinomycin, must not be fed to laying hens.
What to Do in a Coccidiosis Outbreak
Signs include droopy, huddled chicks, ruffled feathers, poor appetite, diarrhea and blood in the droppings. Medicated feed is a preventive; it isn’t strong enough to stop an outbreak. Treat with amprolium in the drinking water following the poultry label: 0.012% for 3 to 5 days (0.024% in severe outbreaks), then 0.006% for another 1 to 2 weeks. If birds are no better after 3 days, have the diagnosis confirmed by a vet. See our Corid dosage guide and coccidiosis in chickens.
While treating with amprolium, avoid vitamin supplements that contain thiamine (vitamin B1), because they can reduce amprolium’s effect.
Helping Chicks Avoid Coccidiosis
- Keep brooder litter dry, and fix leaking waterers quickly; coccidia thrive in warm, damp litter.
- Keep feed and water free of droppings.
- Don’t overcrowd the brooder.
- Clean the brooder thoroughly between batches of chicks.
Free tools
- Chick Temperature & Feed Chart: brooder temperature and feed for each week
FAQs
How long should chicks eat medicated feed?
Many keepers feed it for the first 8 to 12 weeks, the period in which most chickens develop natural immunity with light exposure. Follow the directions on your feed tag.
Is medicated chick feed safe for vaccinated chicks?
It’s not harmful to them, but it can stop the coccidiosis vaccine from working, so vaccinated chicks should eat non-medicated starter.
Can I eat eggs from hens that ate medicated feed?
For amprolium feed at the approved level, federal rules list no egg withdrawal. For any other medication, follow the feed tag.
Does medicated feed prevent Marek’s disease?
No. Medicated starter targets coccidiosis only. Marek’s disease is prevented by vaccination, usually at the hatchery.
Conclusion
Medicated chick starter is a coccidiosis preventive for unvaccinated chicks, not an antibiotic feed. Choose it for unvaccinated chicks, choose non-medicated feed for vaccinated ones, keep the brooder dry, and treat any outbreak with amprolium in the water.
Sources
- Cornell Cooperative Extension (SWNY Dairy, Livestock & Field Crops): Coccidia in Chickens
- 21 CFR 558.55: Amprolium in animal feed (Cornell LII)
- FDA: Fact Sheet: Veterinary Feed Directive Final Rule and Next Steps
- Merck Veterinary Manual: Coccidiosis in Poultry
- AmproMed P for Poultry (amprolium 9.6%) label, DailyMed / US National Library of Medicine
- 21 CFR 558.550: Salinomycin (Cornell LII)
Checked September 2026. Labels change, so always read the label on the product you buy. See our editorial policy for how we research health articles.
