GARLIC (Allium sativum):    Do you use it and is it safe?

"Since garlic then hath powers to save from death, Bear with it though it makes unsavory breath"

Salerno Regimen of Health (12th century)

Quick notes:
Many people use garlic for various reasons, and it is common to feed it to horses, due to claims of everything from worm control to a fly repellent. However, not all claims are justified by scientific research and long-term or high-use of garlic can have side-effects in horses, including anaemia.

More detail:
Garlic has been used in both human and animal medicine for over 3000 years and there are many claims of its benefit against various illnesses and diseases, including as a repellent for worms, flies, (and vampires!). Actual scientific research is more limited, but there are well-designed studies showing that it has many health benefits for preventing and treating various human diseases. From this, people assume that it has exactly the same effects in all animals.

Analysis of the contents of garlic shows that it contains many active compounds and minerals that help with disease and immunity including: anti-oxidants (which help prevent cell damage); compounds that act against infections (such as some bacteria, fungi, and viruses); and compounds that against some parasites. This makes it sound like a miracle cure for all conditions but unfortunately that is not the case.

As well as reports of its effectiveness in some diseases, there are also many reports of the side-effects that it can cause. Garlic has been shown to cause anaemia in sheep, cattle, dogs, humans, and horses, as well as gastrointestinal upsets and other problems (e.g. asthma in humans).

The main toxic effect is caused by organosulphides. The sulphur component not only has some beneficial effects (in the right dose and under the right circumstances) but can also, in effect, poison the horse and cause the side-effects that occur in some people and animals.

What research is available in horses?
The answer is very little. Some products have been tested for some conditions, but there is surprisingly little research into its efficacy (i.e. whether it works) and its safety. Most claims for products are based on people “saying” it works, either because they think it helped their horse or because it works in other species (this is called anecdotal evidence).

  • So, does it really work? I found one study that shows a product acting as an effective expectorant (breaks up mucous in the respiratory tract; similar to ‘cough expectorants’ in human cough medicine) and, at the recommended dose it didn’t cause any side-effects.

However, I couldn’t find any published research (I’m talking scientific research published in recognised journals) to show that it was an effective fly repellent or de-wormer. If you know of any then I am willing to be corrected – please contact me via the Contact Us page with the article name, author/s, and Journal it is published in.

  • So, is it safe? There are very few studies on what dose is safe for horses, and whether a safe dose may depend on how long it is fed for or variations in individual horses. One study showed that anaemia occurred within weeks in horses eating over 0.2g/kg/d; however, studies haven’t been done to find out what the lowest dose is that causes side-effects (i.e. we don’t know what could be guaranteed safe or over what period of time).

Many people claim it is safe because they don’t see any ‘clinical signs’ in their horses i.e. their horse/s appear the same as usual. However, sub-clinical signs (effects that are not seen without further tests) can occur e.g. a horse might have decreased energy levels or stamina, decreased immunity (increased risk of disease), and anaemia. Long-term use may increase the risk of effects (i.e. a cumulative effect as the compounds build up). The compound in garlic can also interact with other herbs and with conventional drugs (ALWAYS tell your vet if your horse is on any herbal product if it needs drugs and/or anaesthesia)

Garlic is mainly fed by horse owners either as a fly repellent, or to help with worm control. Yet there is no evidence that it works (some horses definitely still have flies and worms, though some owners claim their horses are better off); and there is no proof that it is safe for long-term use in the dosages used. Note also that, being a natural product, the amount of compounds will vary in each plant (i.e. some will be ‘stronger’ than others) and that how the product is kept and prepared will also affect concentrations.

To Sum Up:

  • Does it have actual proven effects for some diseases?        Yes
  • Is it proven as an effective fly-repellent?                                    No
  • Is it proven as an effective worm control in the horse?          No
  • Does it cause known side-effects?                                             Yes
  • Might it have long-term effects not seen by an owner?         Yes
  • Do we know the safe dose for short or long-term use?         No

As a vet, do I personally think that garlic can help play a role in fighting diseases in horses in some circumstances? Yes I do. However, please don’t think that just because a substance is natural that it is safe - even vitamin C has side-effects.

Would I feed garlic long-term to one of my horses when it hasn’t been proven to work and a safe dose isn’t known? No I wouldn’t. Please use garlic with care, and monitor your horses for any changes in health if you do use it.

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