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 two and two together. Read More Mysteries Solved to learn how excess dietary potassium affects your horse while the following paragraphs explain how potassium-nitrate can become a major problem.
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 1cm 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 to early winter and 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 onto 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.
Nitrate Toxicity, Sodium Deficiency and the Grass Tetany Syndrome
Excerpts from “Nitrate Toxicity, Sodium Deficiency and the Grass Tetany Syndrome” by Dr. Swerczek, DVM, Ph.D.
Numerous researchers have found that grass tetany occurs most often in older brood cows grazing lush growth of pastures in early spring. 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. Analysis 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 hypomagnesia (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, organs and tissues, the excessive anionic nitrate is removed by the gut, kidneys and mammary glands in lactating animals, as a ionic complex associated with sodium, magnesium and calcium are maintained at physiologic levels and hypomagnesia 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 microflora of the gastrointestinal tract and then the nitrite induces a methemoglobinemia and anoxia. However, it is hypothesised that a much more common mode of nitrate toxicity, and previously not recognised, 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 (micro-organisms that normally grow on dead matter), commensal (organisms that live together but don’t harm each other) and pathogenic (microbes that cause disease) micro-organisms 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 foetuses and the immune system.
These pathogens infect not only the foraging animals but their foetuses. Early and mid-term foetuses may abort, while near-term foetuses 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.
By Jenny Paterson B.Sc
© Copyright 2013
