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Every summer, the warmer weather also brings the nasty little creepy-crawlies. From annoying flies to biting midges, horses are plagued and react with annoyance or panic.
Many horses eventually develop allergic reactions to mosquito saliva, which then triggers sweet itch and can often only be kept under control by covering them with fly or eczema rugs. Even if it helps visually at first: fly/eczema rugs can cause terrible heat build-up on hot summer days, as the horses can no longer regulate their temperature properly by sweating to cool down, which means massive stress for the cardiovascular system.

No effect without side effects

It is well known by now that fly sprays are not always health-friendly, especially if they contain the active ingredient permethrin. Natural essential oils usually only help for a very limited time, as they quickly evaporate as the horse sweats and the effect is gone.

Needless to say, many horse owners are looking for “protection from the inside”, i.e. a “miracle feed” that protects the horse from insect attacks 24/7 ideally.
For this reason garlic has gained popularity over the years. But does it really work? And what side effects does it have? Even with herbal products, there is no effect without side effects.

Garlic is a traditional spice and medicinal plant

Everyone knows garlic from the kitchen and enjoys it’s aromatic and pungent flavour in the dishes. However, garlic has also been used as a medicinal plant for centuries. Its active ingredients have been proven to have anti-inflammatory, antimicrobial, blood sugar and blood pressure-lowering properties. The range of applications is correspondingly broad – from dental inflammation to the treatment of cardiovascular diseases caused by high blood pressure. In ruminants and horses, garlic has been shown to be effective against intestinal parasites, particularly strongyles, which is why it is often included in antiparasitic herbal mixtures.

Fresh garlic against a backdrop of wood
Garlic is a versatile medicinal plant, but it should not be fed in large quantities as this can have side effects.
© Adobe Stock / trotzolga

Garlic in feed unfortunately, is not effective against insects

Although there is a persistent rumour on social media and in equestrian circles that when feeding garlic, it is an excellent insect repellent, unlike its many other proven properties, this is not supported by scientific studies. There are only relatively few studies that work with orally ingested garlic and not with externally sprayed garlic oil, which – like all essential oils – evaporates relatively quickly and therefore does not offer reliable 24-hour protection. A study on humans who were given garlic preparations to eat and then deliberately exposed to mosquitoes found no difference between the test group and the placebo group. Both were bitten the same number of times and the same amount of blood was ingested by the mosquitoes. Not even the consequences of the mosquito bite, in terms of size and itching, differed. What a scientific study, ouch! Studies on cattle in relation to biting flies also found no difference between the test group and the placebo group. It should therefore be noted that garlic may have a small effect on flies in the face if the horses have just eaten the garlic and a corresponding “garlic breath” comes out of their mouths until the essential oils have evaporated. Unfortunately, feeding garlic does not offer any protection against stinging insects.

Feeding garlic to horses is a health risk!

Whilst protection against flies or midges has not been proven, the negative effect of garlic on the horse’s blood values has been known for over 20 years. Feeding garlic in such quantities that horses begin to exude the smell through their skin provokes anaemia, which has a negative effect not only on performance, but also on all metabolic processes in the body that rely on oxygen. Feeding garlic can therefore have considerable negative effects on the overall metabolism, especially if it is fed over longer periods of time, for example throughout the summer. We therefore strongly advise against feeding garlic as an insect repellent: no desired effect, but severe side effects.

What really helps against stinging insects?

All blood-sucking insects have different receptors to identify their potential prey. For a mosquito, it is important to select an animal that provides as many nutrients as possible with its blood meal. This is why there is actually something in the saying that those with “sweet blood” are being particularly often bitten. High blood sugar levels create a very attractive odour that attracts stinging insects like a magnet. Best place to start is here by avoiding overt sugars (e.g. grain, molasses) and “hidden” sugars (e.g. apple pomace, beet pulp, fruit, vegetables, etc.) in the feed. The acidic odour of the horse that accompanies the feeding of haylage is also attractive to insects. If, in addition to a low-starch and low-sugar diet, bitter herbal mixtures are added to the feed, the odour of the horse becomes even less attractive to the flying pests.

In the pasture, for example, you can observe that horses that are fed exclusively on hay, some pasture grass and mineral feed in a equine-appropriate manner and have a handful of bitter herbs in their feed in the evening have significantly fewer fly infestations than horses that have been fed haylage over the winter or those that are given their sweet muesli or mash in the evening.


Feed can indeed be used to combat insect infestation, but the focus has to be on a non-acidic, none-sugar and starch diet, providing the horse with feeds that are natural to their species, so they can protect themselves against insects naturally. Unfortunately, feed containing garlic does not help to repel the burden of mosquitoes and flies, but rather leads to anaemia with all the associated health problems.


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