Common Chicken Illnesses and Warning Signs

Author: Elliott Garber, DVM

Chickens are stoic by nature, so by the time a bird looks obviously sick it is often quite far along. Learning to spot the general warning signs (a hen that goes quiet, stops eating, has a pale or discolored comb, breathes with an open beak, has runny droppings, or turns up dead with no warning) is the single most useful health skill a keeper can build. This guide walks through the illnesses most likely to show up in a backyard flock, what each one looks like from the outside, and where the line sits between “watch and call the vet” and “this is an emergency.” It is written to help you recognize trouble early, not to diagnose or treat, because dosing and medical decisions belong with a poultry-savvy veterinarian.

The general warning signs, before we name diseases

Most of what you will notice is nonspecific, and that is fine. A healthy chicken is bright, alert, active, eating and drinking, with a full crop by evening and firm droppings. Poultry extension services describe the common signs of illness as a departure from that baseline: a bird that stands hunched with ruffled feathers, keeps its eyes closed, stops eating, isolates from the flock, breathes with effort, or shows a comb that has gone pale, purple, or dusky instead of bright red.

Because a single sick bird and a flock-wide outbreak call for very different responses, watch the whole group, not just the one hen you noticed. One bird off feed is a reason to isolate and observe. Several birds coughing, or a run of unexplained deaths, is a reason to stop and call for help before you do anything else. Track what you see over time. A dated note of “comb pale, off feed” in a bird’s health and medical records gives your vet a real timeline to work from instead of a vague “she seemed sick a while.”

Respiratory diseases, and the carrier problem

Respiratory illness is the category backyard keepers meet most often, and it carries a trap: many birds that recover never truly clear the infection. They become lifelong carriers that look healthy but shed the organism and can seed the disease into every new bird you add.

Mycoplasma gallisepticum (MG), the cause of chronic respiratory disease, is the classic example. The Merck Veterinary Manual notes that once infected, individual birds and whole flocks become chronic carriers, and many backyard flocks quietly carry it. Signs include nasal discharge, swollen sinuses (sometimes puffy faces), coughing, sneezing, and watery eyes. Uncomplicated cases are often mild, but the bird stays infected for life.

Infectious coryza, caused by the bacterium Avibacterium paragallinarum, tends to look more dramatic: sneezing, thick nasal discharge, and swelling of the face and around the eyes, sometimes with a foul smell. Extension guidance is blunt about the carrier issue. Birds that recover remain carriers and can shed the bacteria for the rest of their lives, and antibiotics may quiet the signs without ever clearing the organism. Most outbreaks trace back to mixing flocks, when an infected-but-healthy-looking bird is brought in among healthy ones.

Infectious bronchitis, a viral disease, spreads fast through a flock as coughing, sneezing, and gasping, and in layers it often shows up as a sudden drop in egg production and misshapen, soft, or wrinkled eggs. Like the others, recovered birds can continue to shed virus.

The through-line matters more than telling these three apart at home, which you cannot reliably do by eye. Respiratory signs in chickens overlap heavily, and some of the causes are far more serious (see the reportable diseases below). A veterinarian can sample birds and get a real diagnosis. What you control is not letting a carrier into your flock in the first place, which is where quarantine earns its keep. If you keep more than one group of birds, our guide to integrating chickens covers doing that introduction safely.

Marek’s disease: prevented at the hatchery, no cure after

Marek’s disease is a herpesvirus that causes tumors and nerve damage, and it is one of the most common cancers in the entire animal kingdom. The classic presentation is progressive paralysis, often a leg stretched forward and a leg back, along with wasting, and sometimes cloudy or gray irises and vision loss. It usually strikes younger birds.

Two facts define how you handle it. First, per the Merck Veterinary Manual, Marek’s cannot be treated once a bird is infected. Second, it is preventable by vaccination given at hatch, on day one or into the egg shortly before hatching. That timing is the whole point: the vaccine has to get ahead of natural exposure, so it is done at the hatchery, not something you can add later at home. When you acquire chicks, ask whether they were vaccinated for Marek’s, and record the answer. The virus is shed in feather dander and is extremely persistent in the environment, so an unvaccinated bird raised where infected birds have lived is at real risk.

Coccidiosis: the chick killer

Coccidiosis is a gut infection caused by Eimeria parasites, and it is the disease most likely to wipe out chicks. Penn State and other extension programs report that the most severe cases hit birds around three to six weeks old, as young birds build immunity through low-level exposure. Watch for bloody or watery droppings, listlessness, ruffled feathers, huddling, poor growth, and pale combs. It can move fast, and a brooder that goes from lively to lethargic over a day or two should raise this flag immediately.

Warm, damp litter is what lets the parasite bloom, so dry bedding and clean, dry waterers are your main levers. Many keepers raise chicks on medicated starter feed, which contains a low dose of a coccidiostat (commonly amprolium) to help young birds build immunity gradually; extension coccidiosis vaccines given at day-old are another route. These prevention choices, and any treatment of a sick bird, are worth discussing with your vet or hatchery, especially because medicated feed and a coccidiosis vaccine should not be combined. Whatever route you choose, note it in the bird’s record so you are not guessing later. For the broader worm-and-parasite picture in adult birds, see our chicken parasites guide.

Egg binding: a true emergency

Egg binding is when a hen cannot pass an egg that is stuck in the oviduct, and it can be fatal. It shows up more in young pullets laying oversized eggs and in birds short on calcium. The signs, described by poultry extension and the Merck manual, include a hen who is depressed and off feed, straining, walking with a wide penguin-like stance, a distended abdomen, and sometimes labored breathing. She may make repeated trips to the nest with nothing to show for it.

Treat this as urgent. The extension guidance is that a suspected egg-bound hen should be seen by a veterinarian as soon as possible, because a fully obstructed oviduct is life-threatening and attempts to manually extract an egg can rupture it and cause a deadly infection. Warmth and quiet while you arrange care will not hurt, but do not attempt internal procedures yourself. Longer term, adequate calcium (free-choice oyster shell alongside a complete layer feed) and not pushing very young birds into heavy laying reduce the risk.

Crop problems: sour crop and impacted crop

The crop is the pouch at the base of the neck where a chicken stores food before digestion. A healthy crop fills through the day and empties overnight, so a good habit is to feel it first thing in the morning: it should be nearly empty and soft.

Impacted crop is a crop that stays full and firm, packed with feed and often long fibrous grass or litter that cannot move through. Sour crop is a related problem where the crop feels squishy or fluid-filled and may smell fermented and yeasty; it is frequently linked to Candida yeast overgrowth in the digestive tract, which the Merck Veterinary Manual notes can follow antibiotic use or unsanitary waterers. A bird with either problem may go off feed, lose weight, and act dull. Because an impaction and a fermenting sour crop need different handling, and because home fixes can go wrong, get a vet’s read before intervening. Prevention leans on the basics: avoid long clippings of grass, keep grit available so birds can grind their food (our grit and supplements guide explains why this matters), and keep waterers clean.

Bumblefoot

Bumblefoot is a Staphylococcus infection of the footpad, usually starting from a small puncture or pressure sore, that produces swelling, heat, lameness, and often a dark scab on the bottom of the foot. Extension and veterinary sources tie it to poor litter conditions, rough or hard surfaces, and overweight birds. It is common enough that checking feet during routine handling is worthwhile.

Prevention is mostly husbandry: good litter management, smooth well-sized roosts without sharp edges, removing anything birds could injure a foot on, and keeping weight in check. Early or advanced cases warrant veterinary care, because a deep infection can need debridement and antibiotics rather than a surface fix. A clean coop floor is the same investment that prevents a long list of other problems, and our chicken coop guide covers roost and bedding setup.

The reportable diseases you must not ignore

Two diseases sit in a different category because they are federally reportable and can devastate poultry far beyond your own flock: virulent Newcastle disease and avian influenza. Both can cause sudden, high death losses, often with severe respiratory signs, swelling of the head, greenish diarrhea, tremors or twisted necks, and drops in egg production. Critically, birds can die with no warning signs at all. The USDA notes that many birds die without showing clinical signs, and that H5 and H7 avian influenza infections are immediately notifiable to state and federal officials.

Here is the rule that matters: a sudden die-off, or several birds with severe respiratory signs at once, is a reason to call your veterinarian or your state animal health office right away. The USDA’s guidance is that all sudden, unexplained spikes in mortality should be investigated. You are not overreacting by reporting; you are doing exactly what the system is built for, and it is free to do. Do not move birds off your property or bring new ones in while you are waiting for answers.

Biosecurity is the best defense

Almost everything above is easier to prevent than to treat, and the prevention is the same set of habits. The USDA’s Defend the Flock program and extension biosecurity guidance come down to a short list:

• Quarantine new birds for at least 30 days before they touch your flock, and watch them for any signs of illness. This is the step that stops respiratory carriers from getting in. Longer is better.
• Limit visitors, and keep anyone who keeps their own poultry away from your birds. Disease travels on shoes, hands, and clothing.
• Clean and disinfect equipment, and ideally keep dedicated boots or coveralls for your coop. Do not carry gear between flocks without cleaning it.
• Keep feed and water clean and covered, discourage wild birds and rodents, and remove standing water.

The USDA lays out the full routine in its Defend the Flock biosecurity basics. None of it is expensive. All of it beats a sick flock.

Keeping records that actually help

When a bird gets sick, the questions your vet asks are all about history: how long, what changed, which birds, what the droppings looked like, when she last laid. That is far easier to answer from notes than from memory. Keeping each bird’s profile and its record tabs up to date on Creatures turns a stressful “when did this start” into a quick scroll. You can add a health record the moment you notice something off, and set reminders for upcoming care so routine checks and any vaccination history do not slip. Creatures is the records and profile layer, not a substitute for a vet, but good records make the vet visit far more productive.

Frequently asked questions

My hen is sneezing. Is it serious?

It might be minor and it might not, and you cannot tell the cause by eye. Isolate her, watch the rest of the flock closely, and call your vet, especially if more than one bird is affected or the signs are severe. Several respiratory diseases leave survivors as lifelong carriers, so getting a real diagnosis is worth it.

Do I really have to report a sudden die-off?

Yes, and it costs you nothing. A sudden spike in deaths or severe respiratory signs across birds can indicate a reportable disease like avian influenza or virulent Newcastle disease. Calling your vet or state animal health office is the responsible move and protects flocks beyond your own.

Can I treat a sick chicken myself with a remedy I read about online?

Please do not self-dose. Drug choices, doses, and whether a bird needs a procedure are veterinary decisions, and the wrong home treatment can make things worse (or mask a reportable disease). Watch, note what you see, keep the bird warm and separated, and call a poultry-experienced vet.

How do I find a vet who treats chickens?

Not every small-animal clinic sees poultry, so ask ahead. Search for a veterinarian experienced with backyard poultry or avian medicine before you have an emergency, and keep the number handy. Your local extension office can often point you to one.

Do this next on Creatures

Whether you are dialing in flock care, hatching your first chicks, or adding to your flock, Creatures is the records, marketplace, and directory layer to do it in one place.