Wound healing is a continuous process, but classically it has been divided into four phases: the inflammatory phase, the debridement phase, the repair phase and the maturation phase. It is prudent for clinicians to warn owners about these phases so that they will not alarmed by the progress of the healing. This is particularly important if they are dressing the wound themselves.

Inflammatory phase

There is always acute inflammation whether the injury is surgical, physical, chemical or from infection, with an immediate vascular and cellular response. The blood clot will hopefully fill the wound in a sutured wound. The smaller the clot the better, as excessive seroma formation will delay healing from pressure necrosis and bacterial growth. The inflammatory phase lasts approximately 6 h and is often called the golden period, as wounds sutured in this period tend to heal better. The clinician has a dilemma when trauma has occurred: should care be forfeited for speed? Should the wound be sutured immediately or should the animal be moved so that it can be cleaned more thoroughly?

Debridement phase

The second phase begins about 6 h after the incident and lasts up to 12 h, and is mainly a white blood cell response. During this phase it is important that good surgical debridement and haemostasis is carried out. Obviously, good drainage should be arranged, particularly if the wound is infected. Drainage is paramount to ensure good healing.

This next phase normally begins after 12 h and proceeds after barriers such as blood clots, necrotic tissue, debris and infection have been removed. There should be epithelialization, but this may be delayed until a granulating bed has formed.

Unfortunately, with wounds on the horse’s leg granulation bed formation may be too vigorous, so that epithelialization cannot occur quickly enough to cover the excessive granulation tissue, called proud flesh. This overzealous granulation formation is particularly prevalent in thoroughbred and Arab horses. Normally, granulation tissue is proceeded by fibroplasia, which appears after 3–4 days; this is early scar tissue and will continue for approximately 3 weeks. Tensile strength slowly increases as the collagen is laid down; in large wounds tensile strength is still only 80% of the original after 1 year.

Except when granulation is excessive, it is very beneficial, as it allows epithelial cells to migrate. It is very resistant to infection. Wound contraction is centred around granulation, as is collagen formation. However, it does not look very pleasant and owners should be warned. Wound contraction is what owners are looking forward to, but this may be slow or nonexistent if excess proud flesh occurs.

Age and physical status

It is stating the obvious, but younger animals heal more quickly than do older animals; equally, fit horses heal faster than those suffering from systemic disease.

Blood loss

There is no direct link between anaemia and delay in wound healing. However, anaemia resulting from a cause other than blood loss from the wound is certainly not beneficial and should be treated accordingly.

Fig. 12.1. Granulation bed.

Uraemia

Uraemia will certainly delay wound healing, so any kidney disease should be treated and monitored.

Malnutrition and protein deficiency

Horses in this situation will certainly be slower to heal than horses receiving adequate nutrition. Fats can be synthesized by the body from carbohydrates and carbohydrates can be synthesized from protein; however, protein can be made only from ingested protein or its digestive by-products, e.g. amino acids and peptides. Therefore, a protein-rich diet should be fed to wounded horses. Certain amino acids, e.g. methionine, are particularly important for wound healing.

Trace elements

Zinc and copper are especially important for wound healing, although other minerals such as calcium, phosphorus, iron and manganese are also required.

Obviously these are all important for normal body function. However, the fat-soluble vitamins A and E are very important in wound healing. Care should be taken, as excess of either of these vitamins will delay healing. Vitamin K is vital for blood clot formation, while vitamin C is essential for wound healing. Although vitamin deficiency is rare in the horse, chronically debilitated and undernourished animals will obviously benefit from vitamin supplementation.

Veterinary medicines

Certain medicines, e.g. anti-inflammatory drugs, both non-steroidal and steroidal, are known to delay healing, and so their use should be considered carefully. Certain inflammatory responses, e.g. oedema, also delay healing, so their use must be carefully monitored and controlled. A good rule is not to use either, particularly corticosteroids, unless there is a very strong indication, and then only to give them for a short period of time.

We must also consider local anaesthetics; these certainly may delay healing when they are administered into the area of the wound, but in many cases this may be unavoidable. However, nerve blocks should be used whenever possible and the amount of local anaesthetic injected kept to the minimum.

Antiseptic preparations