Lower limb wounds in horses are frequently associated with severe skin avulsion, and excessive contamination. Often these wounds are unable to be sutured and so they are left to heal by a process that is known as secondary intention. Such wounds are predisposed to the development of excessive granulation tissue and prolonged wound healing because of greater wound retraction, slower rates and earlier cessation of wound contraction and slower rates of epithelialisation or new skin growth.
The aim of applying topical medications to wounds left to heal by secondary intention is to manipulate the wound environment. Whilst there is nothing that can be applied to a wound to make it heal faster, the aim of modifying the wound environment is to reduce those factors which can prolong wound healing times such as high bacterial counts and excessive wound retraction. Manuka honey, which is produced in New Zealand by bees that pollinate the native manuka myrtle (Leptospermum scoparium) has been found to have a valuable role to play in the treatment of equine wounds.
The important points to know about Manuka honey are:
- Manuka honey has been found to have potent antibacterial activity against pathogens commonly found in equine wounds.
- The antibacterial properties of Manuka honey are due to the presence of Methylglyoxal (MGO) which is not present in non Manuka honey.
- The UMF rating of Manuka honey relates to its antibacterial activity.
- The higher the UMF rating, the more efﬁcacious the honey is against bacteria.
- For equine wound care select a Manuka honey product that has a UMF of 10 or higher. A UMF of 10 corresponds to a MGO of 263. A UMF of 16 corresponds to a MGO of 572.
- In addition to its potent antibacterial properties, Manuka honey has proven positive effects on the early stages of wound healing.
- The Manuka honey needs to be applied once and ideally twice a day in uncovered wounds and at each bandage change in covered wounds.
- Manuka honey should be applied for the first two weeks of a wound and possibly even longer.
- The application of Manuka honey typically only results in a modest reduction in total wound healing time.
- The precise mechanism by which Manuka honey enhances wound healing in horses is still not completely understood.
Read below for further information.
Selecting The Right Manuka Honey For Wound Care: UMF Vs MGO
Not all honey is created equal and not all Manuka honey has antibacterial properties in therapeutic concentrations.
Some Manuka honey products are labelled with a MGO rating others are labelled with a UMF.
The MGO rating relates to the methylglyoxal content of a particular batch of honey. Methylglyoxal (MGO) has been shown to be the principal antibacterial agent in manuka honey. The higher the MGO rating, the higher the level of antibacterial activity of the honey.
UMF (Unique Manuka Factor) on the other hand is an internationally registered trademark that relates to the honey's antibacterial activity. A UMF rating can only be used by licensed honey producers who meet set criteria which include auditing and monitoring to ensure the product is natural, unadulterated Manuka honey that has unique non peroxide antibacterial activity and is true-to label claim. The antibacterial activity of MGO in each batch of manuka honey is referenced against the antibacterial activity of the antiseptic phenol. The result is expressed to as the ‘unique manuka factor’ (UMF), which is an industry-adopted scale of antibacterial activity. A UMF rating of 20+ is equivalent in strength to a 20% solution of phenol so the higher the UMF the more efﬁcacious the honey is against bacteria. (UMF0–4: antibacterial activity not detectable; UMF5–9: not recommended for therapeutic use; UMF10–15: useful therapeutically; UMF16–30: superior activity with high potency).
Comvita, Happy Valley and Melora are just some of the NZ Manuka Honey brands with UMF ratings. See the UMF Honey Association website for the complete list.
To convert MGO to a UMF rating you can use this handy calculator:
It is important to note that therapeutic Manuka honey has a UMF of 10 or higher. A UMF of 10 corresponds to a MGO of 263. A UMF of 16 corresponds to a MGO of 572.
What About Commercial, Food-Grade Honey?
The antibacterial activity of non Manuka honey relies on the enzyme glucose oxidase which converts glucose to hydrogen peroxide for antibacterial activity. Pasteurisation and ageing reduces glucose oxidase activity and may also negatively affect the activity of other known and unknown bioactive compounds within honey. Furthermore, commonly available food grade multifloral honey is often pasteurised at high temperatures.
It is also important to note that compared to Manuka honey, the bioactivity of food grade honey is unknown and not standardised and therefore any benefits for wound care are likely to be variable at best and more than likely ineffective especially in contaminated wounds.
How Does Manuka Honey Work?
In addition to the antibacterial properties, components within Manuka honey have been shown to be responsible for upregulating the production of key proteins that aid the early phase of wound healing.
Wound care studies have shown that equine wounds left to heal by secondary intention and treated with UMF20 Manuka honey are characterised by decreased wound inflammation, increased angiogenesis (formation of new blood vessels), increased fibrosis and collagen organisation thus promoting a more mature granulation bed earlier in the repair process when compared with untreated wounds. Treated wounds tend to retract less and remain smaller than untreated wounds [which is likely to lead to a smaller amount of scar tissue]. As the wound heals, there is also increased epithelial hyperplasia (new skin formation).
It was also found that UMF 20 is superior to both commercial food grade multiflora honey and UMF5 as a topical treatment or equine wounds.
However, the precise mechanism by which Manuka honey enhances wound healing in horses is still not completely understood.
Rate of Healing.
The application of Manuka honey typically only results in a modest reduction in wound healing time. When the healing time of experimentally induced wounds measuring 2.5cm x 2.5cm were compared, the time to complete healing using UMF20 was 90.78+/- 9.27 days compared to 101.36 +/- 9.25 days for untreated wounds. In other words, a wound that takes around three months to heal may be fully healed 10 days earlier if Manuka honey is used. Although Manuka honey does not drastically alter the time that wounds take to heal, its use can help address those factors that can prolong wound healing times (i.e. excessive wound retraction, high bacterial counts, weak scar formation)
How to Apply and Frequency of Application
Various formulations are available such as gels, impregnated dressings and straight honey.
Ideally Manuka honey is applied twice a day to a wound where finances permit. This is even more important if contact time is likely to be reduced ie if a bandage is unable to be applied to the wound. The research to date would suggest that honey is ideally applied in the early stages of a wound i.e. the first two weeks post injury and perhaps even longer where finances permit.
Bischofberger AS, Dart CM, Horadagoda N et al. Effect of Manuka honey gel on the transforming growth factor β1 and β3 concentrations, bacterial counts and histomorphology of contaminated full-thickness skin wounds in equine distal limbs. Aust Vet J 2016;94:27–34.
Tang AS, Dart AJ, Sole-Guitart A et al. Comparison of the effects of topical application of UMF20 and UMF5 manuka honey with a generic multiﬂoral honey on wound healing variables in an uncontaminated surgical equine distal limb wound model. Aust Vet J 2017;95:333-337