Signs of illness in chickens include wheezing, coughing and general listlessness. Chickens may have trouble moving or may lay down with their wing feathers dragging on the ground and be reluctant to get up.
Respiratory infections are common in chickens, and they may involve mucus buildup in the eyes. This type of infection requires the chicken to be isolated immediately to prevent it from spreading, but it can often be treated with antibiotics.
Lice or mite infestation is another sign of illness. Chickens often refuse to eat or drink when they are sick, and the other hens may suddenly begin to attack them. Sick chickens may stop laying eggs, or their eggs may have thin, brittle shells. The chicken may suffer from diarrhea or may stop defecating entirely.
Unexplained weight loss can be another sign that something is wrong. A suddenly bloated or distended abdomen may indicate several possible problems.
Other than respiratory infections, symptoms of illness in chickens are difficult to diagnose. Very similar symptoms can indicate a variety of problems, and they are usually impossible for even experienced chicken keepers to identify without a veterinarian's help. Owners of sick chickens should try to seek veterinary help as soon as possible.