Here's a hard truth: Every chicken owner, from the backyard coop keeper with six hens to the breeder with hundreds in the barn, has to deal with illness and death on occasion.
Its just part owning chickens.
Prevention Is Your Best Weapon
Probably the best thing is to do everything you can to prevent illness from taking root in first place. This means keeping a close eye on your flock, noting if one looks a little peaked, paying attention to who's eating too much or too little -- those kinds of things.
1. Always have clean, dry food and clean, fresh water for the birds. Disinfect your water and feed bowls from time to time, especially after the summer heat brings out unwanted growth in the watering containers.
2. Keep coops clean and dry. This reduces harmful ammonia fumes, which can cause respiratory illness.
3. Keep an eye on lice and mites, and treat birds and/or the coops on a regular basis. Little chewing, bloodsucking critters can drain the health right out of your birds, making them more susceptible to diseases they might not pick up otherwise.
4. Wash your hands before you go into your chicken pen or coop to avoid transmitting disease. Wash your hands after you're done with the chickens as well.
5. Don't let strangers come into your chicken pens, especially strangers who have their own chickens at home. You never know what germs are clinging to the bottom of somebody's shoes, for example.
6. If you have taken your birds to a county fair or other poultry show, isolate them for two weeks after you return. Gathering hundreds or even thousands of birds into one building can pass illness around faster than a New York minute.
Sick Bird, First Steps
But if you go out to the pen one morning and find a hen all hunched over and ruffled, what do you do?
First, examine your chicken, and write down all the symptoms you can see. Then take a look at the other birds in your flock. Are any of the others exhibiting any signs of malaise? If so, make a note of that too.
If it's just one chicken, separate it from the rest of the flock. This may help keep some of your birds from being infected (though chances are they've already been exposed). Also, chickens tend to pick on a bird that's acting weaker or sick, so you'll want to remove the sick bird from the flock for its own protection. A warm, dry place with fresh water and some food is ideal.
If your bird is eating and drinking, that's a good sign!
Not Getting Better: Who Can I Turn To?
Very few people live in areas with a vet trained in poultry science. Even if you do find someone, veterinary bills can be extremely expensive.
What most of the poultry folks I know do is contact a more experienced farmer for advice. Someone who has hatched and raised hundreds or thousands of birds has seen a lot of problems and will likely have some recommendations for you.
If you don't know anyone, contact your cooperative extension office to find out how to contact an expert.
One book that I really like is The Chicken Health Handbook by Gail Damerow. It is both well-organized and chock-full of good information.
As a last resort, you can try a web search, where you will find a surfeit of advice -- some it good, some of it totally worthless. As you become more experienced in keeping chickens, you will become much smarter about what illnesses and problems you can solve for your chickens.