Let me start by saying headshaking is a rabbit-hole. Thank you very much to Rebecca for your correspondence this week which has been illuminating. We're getting increasing numbers of clients seeking help with this condition. In this email I'm shining a light into the rabbit hole. As you go down each hole the answer seems to be 'we don't know'.
Headshaking in horses can be very distressing and frustrating for both horses and their caretakers. While some head-flicking is a normal behaviour - for mares, for example, as part of establishing dominance - nodding is also normal. Some horses are extremely sensitive to flies, and so the source is obvious.
Headshaking refers more to discomfort or anxiety, and movement that is so frequent and violent that it's interfering with normal activities.
There are many potential causes.
Common Causes:
Ear mites. Nonburrowing psoroptic mites (ticks, and other biting insects) cause an itchy, inflamed ear canal in horses. Some horses show no signs of infection, whereas others may shake their heads and have a drooping ear. Small scabs, hair loss, and/or scaly skin are common. Generally speaking ivermectin can assist and there are topical ear rinses specifically for horses. We will do another email soon about mites, ticks and other biting insects (requested by Skyla this week).
Obstruction in the ear - a foreign object or tumour.
Otitis media (middle ear infection). Because nerves run through the same area to the face you may see drooping eyelids, or facial asymmetry. They may also have trouble with coordination.
Photic headshaking refers to horses who shake their head more in bright sunshine and indicates ocular pain, such as uveitis or glaucoma.
Poll or TMJ (temporo-mandibular joint) pain. This can often be resolved with myofascial release or cranial-sacral body work. TMJ pain can also be related to dental balance.
Higher potassium/nitrogen in grasses and soils.
There is a Horse and Hound article discussing high potassium soils and pasture grasses high in potassium, but I was not able to find the preliminary study they refer to that showed that 70% of pastures where there were headshakers had high potassium soils.
This article on Greenpet also discusses potassium in grasses:
The evidence is accumulating that head-shaking/flicking is another physiological problem and is likely the result of consuming a chronically high potassium diet (re-growth grass, clovers, Lucerne/alfalfa, molasses) exacerbated by pasture ‘spikes’ of both potassium and nitrogen which occur seasonally in the warm, wet, or cool, wet, cloudy or frosty conditions.
Why head-shaking/flicking is ‘seasonal’. Symptoms are noticeably worse in spring, autumn and sometimes other times of the year, depending on the weather. People often report their horses are worse after rain, row, consecutive cloudy days or frosts. This is because grass needs these elements (potassium and nitrogen) for growth and therefore sucks them up at every opportunity. Both are readily taken up into the plant with water after rainfall and tend to accumulate when temperatures are too cold for growth.
These spikes, or changes in the bio-chemistry of the grass, happen especially when you have rye-grass and clover or any species of grass that has been stressed by drought, frosts or over-grazing, when it is in rapid growth mode or when it has been fertilized to increase production.
Rye-grass, clover and lucerne (or alfalfa), are all potent triggers for head-flicking syndrome as is regrowth grass because they are inherently high in potassium and nitrates. All forage is low in sodium. (If your horse isn’t eating any grass, or persists with head-flicking after you have removed the grass, then you would have to look at your hay, or even chaff, perhaps it contains clover or was grown on ground which was heavily fertilized so that it too is out of balance).
Under the above-mentioned climatic conditions, especially those of spring and autumn, grass becomes even higher in potassium but no higher in sodium or chloride. In the absence of sufficient salt (sodium chloride) an electrolyte imbalance occurs which disturbs the stability of cell membranes.
But there is no reference source for this data. Where is the "accumulating evidence"?
That would indicate taking your horse off pasture altogether if they are on ryes, clovers, or other re-growth pastures. You have to feed them something, and it's no help if the hays are just a dried version of the same pastures.
Here is an article we did about the mineral content of various hays with links to a comprehensive database for each hay type.
This study looked at changing salts and electrolytes, and found mixed results that were temporary.
(Salt is important for all horses. A salt block is an easy way to offer it to horses, in addition to adding to their feed.)
Allergies. Some horses respond negatively to a high pollen count, or it's seasonal. In this study 100 headshakers were observed. 11 had identifiable causes, but the others "closely resemble allergic rhinitis in man". Hay fever.
This paper showed that anti-histamines improved the condition. Although, it was a case study of only one horse. Humans take anti-histamines for hay fever. There are side-effects. Here's an overview of pharmaceutical anti-histamines for horses. A natural form of anti-histamine is spirulina, which has just brought in. Look out for more on that in future emails.
Trigeminal Neuralgia: This involves the trigeminal nerve, which becomes hypersensitive and causes pain, leading to headshaking.
There is lots and lots of research on this. Typically, they say - it's a thing, but we don't know how to fix it. Like this one. Although this study does mention to check bloods for deficiencies in magnesium and boron.
Frequently headshaking is referred to as "idiopathic". When you see this word in medicine it literally means "we don't know".
Here is a "we don't know" study from Germany.
It looks like nobody knows conclusively.
You can harvest the low-hanging fruit from what we do know. Check for ear problems, get bodywork done, take them off pasture and feed a low potassium hay, add salt (which all horses need anyway) and magnesium (which many horses are deficient in). Use a uv-eliminating fly veil and confine them to shade during sunshine, add anti-inflammatories like linseed or chia and avoid inflammatories like seeds high in omega 6 (sunflower, safflower, canola, grapeseed). Maybe try an anti-histamine if it's seasonal and you suspect it's allergies?
Finally, if you have found good data or research on headshaking, please let us know so we can share it.
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