Well-kept horses do not become sick very often, but even with a great management program, most horses do feel under the weather at some point in their lives. For this reason, it is good to have an action plan when you detect illness. If your horse or pony appears depressed, lethargic, or unwilling to eat, consult your veterinarian immediately. It is a very good idea to have a thermometer on hand so that you can check for fever as soon as you suspect any sort of illness. Have an experienced horse-person or veterinarian show you how to take a horse's temperature safely. Record your horse's normal resting temperature for comparison.
Should your horse consume something unhealthy (noxious weeds, sand, too much grain etc.) he may colic. Colic is a general term for a horse or pony's stomach ache. Repeated rolling, pawing, looking at and poking his sides, and a refusal to eat are some of the ways that a horse is trying to tell you that he is in pain. Call your veterinarian immediately and follow his instructions carefully until they arrive to treat your horse. All colics should be regarded as potentially life-threatening, and dealt with promptly.
Internal parasites can cause a variety of illnesses and produce a generally poor appearance. Most parasite infections are easily controlled with a program overseen by a veterinarian and administered jointly with the horse owner. Paste dewormers are easy for the horse owner to administer, and feed and tack stores carry many brands of effective deworming products with instructions for their use in a cyclical parasite control program. Read the instructions carefully, and be sure to keep records of the products that you used on a given date. Use a calendar to help you record and plan your de-worming program. If you write down the date and what product you used, you can simply count the weeks forward and write yourself a note on the date when it will be time to deworm again.