Certain wounds are notoriously slow to heal, notably those that can’t be stapled or stitched due to missing skin or the presence of unhealthy tissue. Wounds on the lower leg that are healing by “second intention” — where the surrounding skin cells gradually move inwards — are particularly problematic and healing can take many weeks.
Bacterial infection of wounds can severely delay healing, so, in many cases, antibiotics are key to successful treatment. These are most effective when given immediately following injury and are usually administered by intravenous or intramuscular injection, sometimes followed up by in-feed doses.
Treatment with antibiotics is essential where wounds involve joints, tendon sheaths or body compartments, such as the chest or abdomen. Antibiotics may be necessary in the management of wounds that penetrate the full thickness of the skin, or where a lot of swelling has developed around the area. Protection against tetanus is also important; an unvaccinated horse who sustains even a tiny puncture wound will require both tetanus antitoxin and antibiotic treatment.
When assessing a wound, a vet will determine whether antibiotic treatment is needed. A swab can be taken from the site and sent for laboratory analysis to determine the bacteria present and the antibiotics that will kill them.
Yet antibiotics are not always the answer. There is no point in giving them “just in case”.
In some situations, they will not work — and may even do more harm than good.
Aside from major concerns about resistance (see box , below right), injected or in-feed antibiotics can bring about unwanted consequences. Just as with some people, horses can occasionally suffer an allergic reaction to antibiotics.
Antibiotics can also have an effect on the millions of bacteria in the horse’s gut that are vital for breaking food down and creating energy. While some horses show no ill effects, antibiotics can disrupt the fine balance between the different types of gut bacteria and kill off some of the “good” ones. This allows other bacteria to multiply rapidly and can result in development of diarrhoea or colitis — an inflammation of the gut wall that may be life-threatening and requires urgent and often intensive treatment. It can take several weeks after antibiotics have been stopped for the normal balance of gut bacteria to return.
Another problem that can occur is the development of bacteria within the wound that produce a slimy substance called a biofilm. This creates a shield around the bacteria, preventing antibiotics that are in the bloodstream from reaching and killing them.
In addition to these issues, the cost of giving antibiotics to a horse — which weighs many times more than a person and hence requires more medication — can be substantial.
Marvellous maggots
Where antibiotics are not appropriate for wound healing, what are the alternatives?
There are many products that will destroy bacteria, but there is a risk that they will damage fragile tissues within a wound.
Limited research has been undertaken to determine the effectiveness of some substances, including various herbal products, especially where delicate tissues below the skin are exposed. Until more research is done, it is important to use only those that have been shown to have beneficial effects on the healing of equine wounds.
One simple measure is to stop bacteria entering a wound in the first place. Washing your hands or wearing sterile gloves and covering the site with bandages will help protect the wound from contamination.
Flushing a wound helps to reduce the numbers of bacteria and stop bacterial infection from becoming established. There are many commercial wound cleaning solutions for both human and animal use, designed specifically to kill bacteria.
Saline solutions are most commonly used to get rid of superficial debris and bacteria, especially when flushed onto the wound using appropriate pressure.
Dead tissue is a great food source for bacteria. There are a variety of ways a vet can remove this tissue during the management of chronic wounds: with a scalpel blade or a high-precision surgical tool, or by using one of the specialist cleaning pads designed for human wounds.
Certain substances can be applied to “eat away” at this dead tissue to promote healing, a method called enzymatic debridement.
Maggots have long been used to treat chronic, non-healing wounds where it is impossible or difficult to remove dead tissue.
Anyone who has seen an animal affected by “flystrike” — where maggots invade the tissues, and can do a lot of harm — will know how effectively they can eat flesh.
Maggot debridement therapy involves the use of freshly emerged larvae of the common green bottle fly, produced for the medical and veterinary market by specialist companies. The maggots are treated to remove harmful bugs before being applied either direct to the wound or in a specially designed bag. A dressing over the top stops them leaving the wound site.
The maggots act like a clever surgeon, eating away dead tissue. The fact that they can work their way into grooves and crevices makes them ideal for deep-seated infection of the foot. They also produce natural chemicals that kill bacteria, help stop the formation of biofilms and speed up wound healing.
The sweet spot
Dressings with antibacterial properties are often effective in controlling bacterial infection in chronic wounds. Some are more expensive, but may still be a more cost-effective way of controlling infection than long, costly and unnecessary courses of antibiotics.
Honey was used by the ancient Egyptians for helping wounds to heal and contains many compounds that have beneficial effects, particularly in the early stages. It is important to select medical-grade honey, as this has been treated to remove potentially harmful bacteria and fungi.
Most medical and veterinary honey products contain manuka honey, as this has been the subject of most research. Produced from the manuka bush, found in New Zealand, this substance is given a unique manuka factor (UMF) depending upon how effective it is at killing bacteria. Studies in horses have demonstrated beneficial effects when honey is applied to wounds = healing by second intention. It may be applied as an ointment or within a dressing placed over the site.
While maggots and manuka dressings may not yet be mainstream, they are gaining a valid place in the veterinary toolbox of treatments.
Ref Horse & Hound; 12 April 2018
