Updated: Sep 5
Nitrates Affect Horses Differently to Ruminants
A good subject to understand when grazing horses in winter.
Potassium & Nitrate spikes in the grass occur whenever growth is inhibited - cold or freezing night-time temperatures or lack of sunshine.
Nitrates affect mono-gastric animals like horses DIFFERENTLY to ruminants. In ruminants the Nitrates are rapidly converted to Nitrites which cause oxygen starvation and sudden death. Evidenced by brownish discolouration of blood.
Due to the different layout of the digestive tract Nitrates affect horses differently. Refer the “Mineral Tolerances of Animals” - Non-ruminant animals (including horses) have NO requirement for Nitrates at all “and a toxic effect of acute nitrate levels is generally severe gastritis” (Page 456)
What are the symptoms of nitrate toxicity?
*Note this is referred to as ‘toxicity’ but nitrates are not toxins like mycotoxins and are not eliminated by toxin-binders.
Obviously you should immediately call your veterinarian for any of the following: Symptoms can come and go over weeks - or suddenly
The primary effects of 'severe gastritis' are softening of manure/diarrhea/ weight loss due to loss of protein and inability to produce critical Vitamins (especially B Vitamins), lethargy, loss of appetite, excessive drinking and urinating to excrete the excess urea/edemas (ventral and lower limb swellings).
More serious secondary effects occur under certain climatic conditions which directly affect the nutrient composition of the grass.
They include drowsiness, lethargy, weakness, more serious weight loss, muscle tremors, increased respiratory rates, staggering, inability to chew (like 'lockjaw') and recumbency (lying down flat on their sides), and even grass tetany.
Why is feeding SALT helpful:
There are multiple reasons but here is the relevant one for this subject: Salt is ‘sodium chloride’. Sodium is the positively charged cation for which the negatively charged nitrate ion has the greatest affinity – nitrates can be excreted as Sodium Nitrate.
However, all forage is very low in Sodium and in the absence of sufficient salt in the diet, magnesium and calcium ions are used instead and can thus be rapidly depleted in the efforts to excrete nitrates, causing acute deficiencies of these minerals – the secondary effects listed above.
They may or may not show up in blood tests (eg high BUN -urea, low calcium) because the blood is responsible for keeping the heart beating so is kept 'topped up' as long as possible.
To minimise risk:
If possible, over a week, so it isn’t a sudden change, eliminate the cause (the green grass) and replace with plain grass hay, no lucerne.
If you have no means of doing so feed as much hay every day as the horse will eat.
As explained in the Grass & the Domestic Horse video the metabolic consequences of excesses of potassium and nitrate can be serious -ANY grass of ANY species whether short or lush, if it is green and growing under changeable environmental conditions, poses a significant risk especially where there is rye/clover or capeweed (known to be high nitrates).
References: **“Mineral Tolerances of Animals” (2nd Revised Edition 2005) Page 456 ***Nitrate Toxicity, Sodium Deficiency and the Grass Tetany Syndrome - T.W. Swerczek, DVM, PhD.