I am by no means an expert on chicken illnesses, but I have learned to tell when one doesn’t feel well. It’s kind of like telling when a child is sick. They are lethargic, don’t want to eat, and are willing to let you hold them a lot. Chickens also tend to poof out their feathers. Neither chickens nor young children can explain well what their symptoms are, so observation and isolation from the flock can be useful. This helps them rest calmly in a protected environment. The caretaker can make sure to regularly offer the weakened creature food and water, while various bodily functions can be more accurately evaluated. (The chicken below is healthy but wonders why we need to take pictures of it in a box. My daughter is demonstrating one way that a small chicken likes to be carried).
A cardboard box inside of a dog kennel works well for a chicken hospital (original meaning of the word “hospital” is “shelter for the needy”, which did not imply large institution). The cardboard box can be lined with a couple layers of newspaper, that needs to be changed daily. Small bowls with grain and water can be placed close to the chicken. Any spillage is contained by the box. A smallish box also tends to make the chicken feel safer. The lids can be closed at night to provide darkness, even if the lights are on in the house. Having the box in the kennel means I can leave the box open as much as the chicken and I like, and I don’t have to worry about the healing chicken escaping. It also means that the chicken is safer from our cats and dog.
If you don’t have or don’t want to purchase a dog kennel, it’s not too hard to build a small cage with some scrap wood and chicken wire. Make sure to give it an easily removable lid. My husband built me two of these a couple of years ago for mobile pens for my growing chicks. My wire cages are larger than I would want in the house, but if you know the corner that would work for your situation, you could build one to fit. The mobile pens work best with no floor outside, so if you want to use it inside and outside, a box would still be needed. Just keep in mind that the sizes of your boxes may vary. The boxes should be thrown away after each chicken.
Our dog kennel is in the greenhouse adjacent to the kitchen, which means it is slightly cooler or warmer than the rest of the house, depending on the season. It also has lots of windows for ventilation, as needed. Even though I am moderating extremes in temperature for the sick chicken, I don’t necessarily want them getting too comfortable, so that going back outside is a shock to their system. The proximity to the kitchen means I will see the chicken as I go about the day. We only use the kennel for the dog when we leave the house without her. If we need to do this, we can remove the boxed chicken, make sure the box is closed, and just set it somewhere else in the greenhouse until we get back.
We have used this hospital set up for everything from rehabilitating a rooster with a broken leg to nursing hens that seem like they have the flu. In the final photo, a Barred Rock hen is getting some sunshine during her convalescence after a fox attack. I’m not one to subject my children, or my chickens, to unnecessary medicines and antibiotics that may upset the body’s efforts to heal itself. Besides, medicine cannot replace the tender ministrations of a diligent caretaker in a private setting.