Wound first aid
Keep calm; get the horse to a situation where it is quiet and safe (for the horse and people about it); and call for help early if required. Severe injuries require veterinary help; both for decisions and treatment. If the situation is dangerous, do not approach the horse. Once the horse is restrained safely, assess the extent of the injury (is it just bruised, cut deeply through the skin, is there deeper damage likely, is it bleeding profusely?) and treat accordingly.
Prevention revolves around being aware of possible accidents, and trying to avoid them. This includes having a well controlled horse, having good sound equipment, and having the horse in a safe environment. Despite having all of the above, accidents still happen.
Treatment depends on the injury, its location, and the severity of the injury. Bruising without skin broken is best treated with ice compress (up to 30 minutes at a time, 3 - 4 times a day for 2 - 3 days) and anti-inflammatory drugs. Bruising with skin broken and/or puncture wounds, is one of the more dangerous wounds as they are very prone to infection and tetanus. Get veterinary attention. Punctures on their own (no or little bruising) appear so minor, yet often have the worst outcomes. Infection is very common, often appearing 1 or more days later (swelling, heat, and lameness); and foreign bodies are often sealed inside the puncture. Get your vet to check these injuries. Cuts involve bleeding and horses have a lot of blood, so what appears serious is often not. Stop bleeding by applying pressure to the area with a clean cloth. Bandage it on tightly if possible, and gently release the pressure every 10 minutes to allow circulation for a minute then re-apply pressure; continue this until the bleeding is under control. Whether these wounds should be sutured will be decided by your vet and it will depend on the location of the wound, how old it is, how contaminated it is, what has been done to the wound, etc. Many wounds are best left unstitched for best healing, even though initially it will look better for you if it was. All wounds should be thoroughly cleaned and flushed (with clean water or saline solution), then treated with a topical ointment, powder or spray if not stitched, and bandaged if appropriate. If you think the wound will be stitched, flush and clean the wound but do not apply medication before your vet arrives. If you suspect deeper injuries (eg to a tendon or joint), get your vet to assess the injury