Chicken Disease Encyclopedia

Pale comb is a symptom, not a disease. Common drivers are heavy mites or lice (anemia from blood loss), internal worms, broody hens losing condition, or chronic disease.

A slow spreading virus carried by mosquitoes. Dry form (scabs on comb and wattles) usually heals on its own in 3 to 4 weeks. Wet form (mouth and throat lesions) is dangerous.

Cold and humidity damage exposed tissue. Tips of large combs and wattles go black or gray. Wet bedding plus cold makes it much worse than dry cold alone.

A blockage of fibrous material (long grass, straw, bedding) jams the crop so food cannot pass. The crop stays full and firm by morning instead of empty.

A yeast (Candida) overgrowth in the crop, often following antibiotic use, spoiled feed, or an impacted crop. Crop feels like a water balloon and the bird's breath smells like sour milk.

A protozoal gut infection that destroys intestinal lining. Bloody or mucousy droppings in a young chick are nearly always coccidiosis. Fatal if untreated.

Common internal parasites that steal nutrients and cause weight loss, pale combs, and droppy lay. Most free range flocks have a low level burden, problems start when it gets out of hand.

A normal annual feather replacement, usually in fall as daylight shortens. Birds look ragged, stop laying, and act subdued. Not an illness.

Lice live on the bird, mites often live in the coop and feed at night. Heavy loads cause anemia (pale comb), feather damage, and a stressed flock that stops laying.

A staph infection that enters through a cut or pressure sore on the foot pad. A black scab is the calling card. Easy to treat early, ugly if left.

Tiny mites burrow under leg scales and raise them up, leaving crusty white or yellow buildup. The legs look thick and lumpy. Treatable but uncomfortable.

Paralysis caused by a toxin from Clostridium botulinum, usually picked up by eating decaying animal matter or wet rotting feed. Limp paralysis that creeps up the body is classic.

A herpesvirus that causes paralysis (classic split leg posture), tumors, and a gray eye. No cure. Survivors stay lifetime carriers. Vaccinate chicks at hatch to prevent it.

Neurological signs caused by vitamin E and selenium deficiency, head trauma, or sometimes Marek's. Pure vitamin cases often reverse fully with treatment.

An egg gets stuck inside the hen. She strains, walks upright like a penguin, and stops eating. Untreated egg binding past 24 hours is often fatal.

Yolk material misses the oviduct and drops into the abdomen, triggering infection. The hen develops a swollen belly and waddles. Often fatal even with treatment.

An occasional soft egg is normal for new or stressed layers. Persistent soft shells point to a calcium deficiency, illness (often IB), heat stress, or aging reproductive tract.

A yeast and bacterial inflammation of the vent. Yellow paste, fishy smell, and a generally unhappy hen are the classic combo.

Part of the reproductive tract pushes outside the vent. The exposed tissue attracts pecking, which can kill the hen quickly. Isolate first, treat second.

A fungal lung infection from inhaled Aspergillus mold spores in damp bedding or moldy feed. Often hits chicks in brooders. No discharge, unlike bacterial respiratory disease.

Highly pathogenic avian influenza is a reportable disease that can wipe out a flock in 48 hours. Dark combs, swollen heads, and sudden death are red flags. Report immediately.

Chickens cannot sweat. Above 90 F they pant and dump heat through their comb. Heavy birds, dark feathered birds, and those with large fluffy bodies are most at risk.

A very contagious coronavirus of chickens that causes mild respiratory signs in adults and lasting damage to the egg making system, soft or misshapen eggs are a giveaway.

A fast-spreading bacterial respiratory infection that causes swollen faces, smelly discharge, and one-sided sinus swelling. Recovered birds often stay lifetime carriers.

A severe herpesvirus that attacks the windpipe. Classic signs are gasping, neck stretching, and coughing up bloody mucus. Often fatal. Survivors stay lifetime carriers.

A slow-burning bacterial respiratory disease that produces classic foamy eyes and a rattling chest. Birds carry it for life and shed it under stress.

A reportable viral disease with respiratory, digestive, and neurological signs. Virulent strains kill flocks fast. Contact your state vet or USDA APHIS at the first suspicion.

Once chickens see blood they will not stop. Triggers include overcrowding, boredom, protein deficiency, or a sick bird singled out by the flock. Isolate any bleeding bird immediately.

Bites, scratches, or punctures from raccoons, dogs, hawks, foxes, or other birds. Chickens are stoic, the wound is often worse than the bird looks at first.