Some horses seem to be accident prone. It can be very frightening to go out and see that your horse or pony has a wound. However careful we are with our paddocks, stables and yards, it seems that some horses are able to find something to injure themselves on, sometimes with disastrous consequences.
If there is any chance that a joint or tendon may be affected by a wound, it is always better to get veterinary attention sooner rather than later. It is often small, deep puncture wounds that cause problems.
There are a lot of ‘synovial structures’ in the lower legs. This is the term used for joints and tendon sheaths (the cushioning layer around some tendons).
Once these become infected and inflamed there is a potential for permanent damage to occur. Joints often have ‘pouches’, which means that the joint pocket can be some way from what we think of as the joint. A wound that is anywhere near a joint should be examined by a vet to see if the joint has been affected.
Bleeding from wounds
Often it can look as if a lot of blood has been lost and this is, of course, of great concern – but horses do have a lot of blood. Around 8% of a horse’s bodyweight is blood, so a 500kg horse has about 40 litres. Something to bear in mind is that a 500kg horse can lose 6-8 litres of blood before it is physically affected, and 12-16 litres before the loss becomes life-threatening. However, bleeding should still be stopped (if you can do so safely) by applying pressure to a wound while waiting for the vet to arrive.
How do wounds heal?
Wound healing happens in several different overlapping stages. It starts with an acute inflammatory phase which lasts about 4-5 days. This is when the body sends inflammatory cells to the site of the wound to try clear up any bacteria or dirt contamination. This is why in the first few days the dressing often gets soaked through very quickly with what we call exudate, which is fluid and dead cells all aiming to clean the wound and remove contamination. The dressing needs to be changed more often during this phase.
Next is the proliferative phase, which is when granulation forms. This is the pink sponge-like tissue that rapidly fills in the wound – too much of this is what we call proud flesh.
Epithelialisation and contraction also now occur. Contraction of the wound makes it rapidly smaller – this more easily happens with wounds on the body, as there is more skin available compared to the legs. Epithelialisation is what we call the very thin layer of skin growing in from the edges of the wound. This takes time to grow across the wound and explains why wounds on the legs, which can’t do much contracting, take longer to heal.
Epithelialisation can be a difficult process and can be hindered by several factors. If the wound gets too dry, the process will slow down. Proud flesh which bulges out over the surrounding skin will also stop this layer of skin closing over the wound. Even a dressing which sticks to the wound can result in this layer being pulled off, with a bandage change slowing down the healing.
Finally, once the epithelialisation has closed over the wound, we get remodelling. This minimises scar size and can still be happening three weeks to more than a year after the wound has happened. (This may also explain why some ointments appear to reduce a scar – it could be that remodelling was minimising the scar anyway).
Factors which delay healing
There are a number of factors that will delay wound healing, and often these are more common in leg wounds. These delaying factors can result in either a wound that is slow to heal or one that develops proud flesh. The following are 10 main factors that can delay healing:
1. Infection – by bacteria, viruses and fungi will all delay healing. A wound must be cleaned thoroughly and a good bandage will prevent reinfection. Antibiotics may be used by your vet if they are indicated.
2. Movement – this is particularly important on the legs. Movement makes it harder for the wound to fill in, delays healing and can often result in proud flesh. Confining the horse to a small area, using a thick padded bandage and sometimes even a cast are all ways that movement is restricted to encourage healing.
3. Presence of a foreign body – this just means something present in the wound that shouldn’t be there. Soil or small splinters of wood are good examples; a clean wound is vital.
4. Presence of necrotic (dead) tissue – this is skin, muscle or tendon that has lost its blood supply and dies off, then acts as a foreign body. Vets will often cut off flaps that have lost the blood supply as although it makes the wound bigger to start with, removing dead tissue actually allows healing to progress. Sometimes the flap will be left in place initially to protect the rest of the wound. A skin flap may also trap dirt at the junction with normal skin, which may be another reason for it to be removed.
5. Continued trauma – this is quite obvious but a wound caused by something rubbing won’t heal if whatever caused it is still rubbing.
6. Human factors – something that we might do to the wound that delays healing. It can mean the wrong dressing, a bandage that isn’t changed often enough or is too tight, or the use of a topical ointment that inhibits rather than helps healing.
7. Large deficit – a large wound with a lot of tissue missing will take longer to heal as the granulation tissue has to fill in the gap. The blood supply also has to grow back.
8. Poor blood and/or oxygen supply – blood and oxygen are both important for healing. It is thought that using a dressing which prevents oxygen getting to the wound can encourage the formation of proud flesh, so using a breathable dressing is advised.
9. Health status of the horse – the age of the horse affects healing (young horses usually heal better than older ones); whether it is a pony or a horse affects healing (ponies usually heal better than horses) and if the horse has Cushing’s syndrome then healing can be delayed.
10. Sarcoid – wounds can turn into sarcoids; we don’t know if this is because flies which can carry a virus (bovine papillomavirus type1, BPV) are attracted to the wound and deposit the virus there, resulting in a sarcoid, or whether it is actually something in the healing process that changes and causes a tumour to form instead. The start of a sarcoid can look like proud flesh, so it can be difficult to tell early on if this has happened, but it is something to bear in mind in a non-healing wound.
Common complications are proud flesh and infection. With any complications of wound healing, you should seek veterinary advice. Infections will need to be treated, proud flesh removed and then if any of the other above factors are present these will need to be managed to allow healing to take place.
Hopefully, by having an understanding of how healing occurs and also what stops or inhibits it, you will be able to manage any wounds you are unfortunate enough to encounter and so keep conditions as ideal as possible for healing.
When to call the vet urgently
As always call your vet for advice on any wound, but you need to call immediately if:
- the wound is deep
- if there is a lot of bleeding
- the wound is anywhere that could be near a joint or tendon or other vital structure on the legs
- if the wound involves the eye/eyelids
- if the wound is into the chest or abdomen
- if it involves other vital parts eg. sinuses, mouth, axilla (equivalent of our armpit), groin, neck etc.
- if the horse is showing signs of lameness
- if tetanus vaccination is not up-to-date.
*This article first appeared in the August 2015 issue of NZ Horse & Pony magazine