Any horse that lies down for longer than 24 hours for any reason is considered to have a poor prognosis. Horses simply are not made to be down for any length of time. Their massive weight causes damage to muscle, tissue and skin. Lungs and heart do not function well.
Never nurse a down horse for extended periods of time without talking to your vet and knowing what you are treating and what you expect to gain by this approach.
The horse should be maintained on deep bedding (shavings, soft sand or straw) whenever possible. Generally, horses do better when sitting up on their chest (sternal) than laid out flat on their sides for extended periods (lateral).
Down horses that are flat out should be rolled from one side to the other (according to your vet's recommendation) every few hours to help reduce the development of sores and improve circulation.
If the weather is cold, cover them with a blanket. If it is hot, provide a misting fan, shade or both. If they are laid out flat on their sides frequently move their head, and remove or manipulate their halter to help prevent facial paralysis. The down limbs should be pulled forward as far as possible. If the horse cannot maintain sternal position (on the chest), then bales of straw might be used to prop behind the rib cage and shoulder.
You can perform a limited assessment of a horse's health while they are lying down, just always work from the back of the horse. Look at the horse’s eyes, gums, and listen to the heart. Even if you think your horse is unresponsive, look at their eye? Are they blinking? Move your hand quickly towards your horse’s eye. Do their eyes blink or move?
Sores may be treated with basic wound care and topical antibiotics. Some may become infected and require additional care. In that case, further local treatment and possibly systemic antibiotics and bandaging may be needed.
Tips for safety & Success
A disease process that causes a horse to lie down for any considerable period of time is usually serious, so call your vet right away.
A down horse is dangerous. You must stay out of the way of their limbs at all times. Do this by staying behind the horse's back, neck and head. Stay away from their legs.
A down horse can roll very fast as well, trapping you underneath them or inadvertently kicking you when they roll over. Stay on your toes, ready to move out of the way quickly.