I now believe various degrees of grass tetany is the fundamental root cause of most of the health and behavioural issues with our horses. Because the symptoms are so wide and varied it has taken a long time to put 2 & 2 together.

For those who get bamboozled by science, in very simple language, the cool, cloudy, wet weather of spring and autumn (including frosts and freezes) cause acute spikes of potassium and nitrate in the grasses our horses are eating. This grass may only be 1 cm long but under these climatic conditions, it can have a drastic effect on your horse. (This effect can be made worse by high protein feeds as protein converts to nitrate which has to be somehow eliminated at the expense of your horses calcium and magnesium supply).

Fertilised rye-grass and clover are the worst for this scenario but ANY grasses under the 'right' conditions can have the same effect. This is why it is so important to have somewhere you can keep your horse completely OFF the grass during these times. (Early spring, autumn - early winter, drought breaking rains).

All the literature I have read says that horses don't suffer from nitrate toxicity like other stock. Indeed I have a copy of a letter from a prominent Canterbury Vet who says that there is no evidence that horses suffer from grass tetany at all! He couldn't be further wrong!

As the following paragraphs explain it is not the nitrate directly but the fact that it enters the system as potassium nitrate. The excess potassium and toxic nitrate is excreted by latching on to calcium and magnesium indirectly causing a serious deficiency of these vital minerals and all the associated health and behaviour issues (an extensive list!).

For those who need a more scientific explanation: (Whilst the article refers mainly to cattle, Dr Swerczek has since done trials on horses which prove they are affected by the same process. Grass, even if it is very short, can be dangerous under certain conditions, which include a drought breaking rain). Also Google "Don't Short Salt", it is brilliant.

Excerpts from "Nitrate Toxicity, Sodium Deficiency and the Grass Tetany Syndrome" by Dr T Swerczek D.V.M

Numerous researchers have found that grass tetany occurs most often in older brood cows grazing lush growth of pastures in early spring, and the triggering of the grass tetany syndrome includes environmental conditions of cool, cloudy and wet weather, promoting rapid, lush growth of cool season grasses. These environmental conditions, which also include frosts and freezes, will cause acute spikes in potassium as well as nitrate in affected growing pastures. Analyses of these affected pastures during and after periods of frosts and freezes revealed elevated levels of potassium and nitrate.

Nitrate in the form of potassium nitrate is reportedly the form which herbivores are exposed to nitrate. During periods of stress to pastures forages, the acute spike in potassium and nitrate is seemingly causing an electrolyte and mineral imbalance in affected herbivores. If nitrate is excessive, a hypo magnesia (magnesium deficiency)and/or hypocalcaemia (calcium deficiency) may develop as the body is eliminating magnesium and calcium with the excessive anionic nitrate. However, if there is adequate sodium in the diet and organs and tissues, the excessive anionic nitrate is removed by the gut, kidneys, and mammary glands in lactating animals, as an ionic complex associated with sodium, and magnesium and calcium are maintained at physiologic levels and hypo magnesia and/ or hypocalcaemia will not occur.

For this reason adequate levels of sodium in the body and ration will lessen or prevent the drastic effects of nitrate toxicity. Also, it explains why adequate sodium in the diet will aid in the prevention of grass tetany, which is associated with high potassium and low magnesium levels. It is apparent that nitrate toxicity in herbivores is much more prevalent than previously reported.

A well documented form of nitrate toxicity occurs in ruminants when nitrate is converted to nitrite by the micro flora of the gastrointestinal tract and then the nitrite induces a methemoglobinemia and anoxia. However, It is hypothesized that a much more common mode of nitrate toxicity, and previously not recognized, is when nitrate toxicity induces a severe electrolyte and mineral imbalance in ruminant and non-ruminant herbivores. This form of nitrate toxicity is an important factor in the pathogenesis of the grass tetany syndrome and likely other syndromes in herbivores, including reproductive disorders in all herbivores, including horses. Seemingly, adequate dietary sodium not only protects against nitrate toxicity, but also aids in the prevention of the grass tetany syndrome in herbivores, and other metabolic and reproductive disorders induced by nitrate in herbivores.

The high nitrate in the milk may also explain why neonates seemingly are affected with a multitude of opportunistic gastrointestinal diseases, including gastric ulcers and other intestinal disorders. Conversely, dams fed a low protein diet and adequate sodium rarely have neonates suffering from these gastrointestinal disorders.

Potassium promotes the overgrowth of saprotrophic (microorganisms that normally grow on dead matter), commensal (organisms that live together but don't harm each other) and pathogenic (microbes that cause disease) microorganisms in plants, especially plants damaged by droughts, frosts and freezes. Thus, such forages become the source of many opportunistic, potentially pathogenic bacteria and fungi.

After ingesting them, livestock face an overgrowth of opportunistic, pathogenic organisms in the gut. The organisms rapidly proliferate to produce toxic by-products, like excessive ammonia, which is acutely toxic to fetuses and the immune system. These pathogens infect not only the foraging animals but their fetuses. Early and mid-term fetuses may abort, while near-term fetuses may suffer premature birth, and/or septic weak neonatal birth.

Similarly, it's felt that high-potassium forages encourage excessive growth of endophytic and other pathogenic fungi, especially in fescue and rye grasses. The toxins these fungi produce add to the reproductive problems in cattle and horses.

More Mysteries Solved

Hyperkalemia means too much potassium! This is another major mineral imbalance we are inadvertently imposing on our poor horses. It is very closely tied in with calcium/magnesium imbalances we have learned about already. The more reading a person does on the subject the more a person becomes convinced that this is the root cause of many of the conditions afflicting our pasture fed horses.

Think about the fact that many horses are completely OK any time grass isn't growing (winter and drought) but the nano-second that there is a flush of growth all of the following start to happen: 

The myriad of symptoms we lump together and call 'spring fever'.

Acidosis

Head-flicking

Laminitic attacks

(often accompanied by or preceded by the myotonia and laboured breathing)

Racing around the paddock for no reason

'Out of the blue' uncharacteristic, violent behaviours

Stiffness, inability to bend, tendency to 'run-off'

Magnesium deficiency

Tetany (including convulsions and death in extreme cases)

Excess potassium interferes with calcium and magnesium absorption. On top of the fact that soils averagely lack these minerals and rapid growth outstrips uptake, absorption of what little magnesium is ingested can be sabotaged at the last minute by the excess potassium. 

This information makes for yet another chapter in "The Case Against Rye- Grass & Clover for Horses" saga. Rye-grass and clover have an exceptional affinity for being high in potassium, especially when fertilised with nitrogen, urea, or super-phosphate which induce rapid growth during which plants accumulate potassium in their growth tips. Hence the 'worst case' horses are those grazed on dairy pastures which can have a potassium content up to 5% or even higher. Legumes, like clover and lucerne, are also very prone to being high in potassium providing a likely explanation for why they are known to 'send some horses nuts'.

Here is an outline of how sodium and potassium work on a cellular level:

"Potassium is concentrated in the fluids inside the cell wall and sodium is concentrated on the outside of the cell. Each time the body has to use a nerve or a muscle, potassium is ejected from the cell and the change in ionic balance sparks an electrical impulse causing the cell to react. It does so by conducting a brain impulse, if it is a nerve cell, a contraction if it is a muscle cell.

Once the reaction has occurred, the original cellular balance between sodium and potassium is restored and the nerve or muscle will relax (potassium's relaxing effect inside the cell is similar to magnesium's outside the cell)

From Minerals the 'Metabolic Miracle Workers' by Dr Robert Erdman & Meiron Jones.

A diet that is too high in potassium means that the extracellular fluid is permanently high in potassium. This upsets the delicate sodium:potassium ratio and amongst other things, putting it simply, the nerves and muscles cannot relax.

There is even a condition called 'Potassium Aggravated Myotonia'. Myotonia means 'failure of the muscle to relax' and this is caused by this high potassium on the outside of the cells. 'Potassium Aggravated Myotonia' exactly describes one of my own horses and many of the horses I meet on my travels.

It exhibits as a stiffness (can't bend, stiff movement, back legs together when cantering, continual cross-firing or disuniting, a tendency to run off. They warm out of it to an extent). Affected horses are 'on edge', often volatile, very anxious, sensitive and rigid. Some horses get noticeably worse each time the grass has a little growth spurt. Some horses are in this state permanently due to being out on potassium rich pastures 24/7.

Hyperkalemia (too much potassium) compounds magnesium deficiency and symptoms include(3):

Tense, hard muscles, twitching around the flanks and ribcage

Bouts of colic

Laboured breathing

Skin tingling

It just could be possible that head-flicking could be added to the list. After all it is 'involuntary repeated firing of the trigeminal nerve in the head) We know that removing rye-grass/clover and lucerne from the diet reverses this condition. Perhaps this is because removing these plants from the diet drops potassium levels back down to where they should be.

Feeds that contribute to the too much potassium syndrome include:

Any green, growing grass

Especially if it is rye-grass or clover

Especially during rapid growth after fertilisation with nitrogen, super-phosphate, urea

Especially in drought-breaking conditions

Especially if the diet also contains other feeds which are inherently high in potassium:

Lucerne, chicory, kelp, molasses

Ginseng, dandelion, nettle, sage, yarrow, rosehips, slippery elm, garlic, plantain, echinacea, chamomile, comfrey

Soya bean Meal

Whilst all of these feeds and herbs can have great benefits, they need to be taken into account when arriving at the sum-total potassium content of your horse's diet.

In the case of horses, potassium is very easily obtained in the diet and is more often than not present in vast excess. Therefore it is important not to add more via the horses Vitamin & Mineral supplements.

Sure the recommended daily amount is 25gms/day for a 500kg horse (1) but 10kgs rye-grass in vegetative state @ 3.34% potassium giving them a whopping 33.4gms(1) ½ kg lucerne chaff @ 3.21% giving a further 1.6gms(1) 10kgs of grass hay would supply 19.7gms(1) Plus if you are also feeding a supplement containing potassium..., or adding cider vinegar, kelp, garlic, many herbs like comfrey, chamomile, echinacea, Chicory, plantain...

On their own, (or if your horse is not eating the high-powered pasture as well), these feeds can have benefits but they need to be included in the total potassium content of your horse's diet. Check that your vitamin and mineral supplement does not contain potassium but also that it does contain sodium which is very necessary to help balance the high potassium intake. A lack of sodium (salt) reduces urination which is how the horse is supposed to excrete this excess potassium.

Interestingly enough soaking hay reduces its potassium content by about 50%.(2) The only time there would be a necessity for administering potassium would be when the horse is in work and sweating heavily. Hay still contains potassium in good quantities, so no need to worry if your horse is getting little or no grass, they'll be getting the 'right amount' from good grass hay.

Interestingly, humans ingest far too much sodium and not enough potassium. Most processed foods are full of sodium because we like the taste, and cooking food depletes potassium. So we end up with the opposite problem to our horses!

 (1) The National Academies 2007 Nutrient Requirements of Horses

(2) Katy Watts www.safegrass.org 

(3) Hyperkalemia JOYCE C. HOLLANDER-RODRIGUEZ, M.D., and JAMES F. CALVERT, JR., M.D. Oregon Health & Science University, Portland, Oregon

by Jenny Paterson B.Sc (New Zealand) © Copyright 2009