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The understanding of the health benefits associated with a high-fiber diet consisting of grass and hay, as opposed to concentrated feed, has gained widespread recognition. Good quality hay is just one of the two fundamental nutrients; the other often leads a rather quiet and sometimes neglected existence: water.

Why is nitrate problematic?

Nitrate in itself is largely harmless. The term “nitrate” specifically denotes salts and esters derived from nitric acid. It serves as a nitrogen supplier in the soil, facilitating the production of ample protein for plant growth. On soils with low nitrate content, plants tend to be stunted and resilient, whereas nitrate-rich soils foster lush and vibrant green growth.

Nitrate poses a concern when it enters the body. This occurs primarily through conversion to nitrite in the intestine. Nitrite is absorbed and enters the bloodstream. Here, it changes the red blood pigment, hemoglobin. This is essential for transporting oxygen from the lungs to the tissues, as all cells in the body require oxygen for survival. When nitrite alters haemoglobin, it forms methaemoglobin, resulting in tissues receiving insufficient oxygen, as methaemoglobin no longer binds to oxygen. Furthermore, nitrite can react with amines, forming compounds known as nitrosamines. These compounds are suspected to be carcinogenic, a fact supported by evidence from animal experiments.

In many countries, drinking water is subject to rigorous quality controls

In many countries, drinking water undergoes stringent controls to ensure compliance with safety standards and prevent the surpassing of threshold values for toxic substances. This includes nitrate levels, which, for instance, must not exceed 50 mg per liter in drinking water in Germany. Nonetheless, there’s a distinction between water suitable for animals and our human drinking water. For what’s termed “animal drinking water,” the nitrate content can go up to 200 mg/L (in Germany).

Unfortunately, in many stables, water quality is often neglected, with irregular testing or monitoring being the norm. Generally, supplying horses with standard tap water ensures their safety. It originates from the supply pipe connected to the residential building, directly from the nearby waterworks. The limit values are regularly monitored here.

It is prudent to inspect the plumbing systems in very old farms. Decades of extensions and renovations on many old farms have resulted in a diverse mix of water pipe materials. In the past, iron, lead, or zinc pipes were commonly used, which may sometimes result in residues in the water. For this reason, plastic pipes that are water-neutral are generally used today. While such materials do not increase the nitrate content of the water, they can still have a negative impact on its quality, potentially affecting the health of the horses.

“Dead ends” can also pose a problem, referring to inactive sections of water pipes where water stands instead of flows. Microorganisms, in particular, can thrive in such areas, multiplying undisturbed and potentially contaminating the drinking water.

This can lead to significant differences in quality between the water supplied by the waterworks and the water that comes out of the tap or drinking trough.

However, due to the high consumption, horse troughs are often supplied with well water rather than the more expensive municipal water. And if you do, it’s crucial to regularly test your water yourself, as the quality can fluctuate significantly.

Rainwater is no alternative

It’s important to clarify from the start that rainwater is not a viable alternative for water supply. For one, it lacks minerals, which can pose a long-term risk to the animal’s health and result in a significant mineral deficiency when ingested. This could potentially be compensated for with a high-quality mineral supplement. However, depending on the type of roofing material used from where the water is collected, there’s a risk of additional toxins being introduced through leaching. The traditional “roofing felt” remains a concern in this regard, as do older Eternit roofs. Moreover, roofs are often tainted with bird droppings, a sight you wouldn’t want in your horse’s drinking trough. Thus, it’s preferable to construct a pond in a trench that directs rainwater from roofs and paths to seep away, keeping it away from the water troughs used for drinking.

Rain runs over corrugated iron roof into gutter
Rainwater is not a suitable alternative for water supply.
© Adobe Stock / Kev

Lots of animals and agriculture = lots of nitrate in the water

One of the major contemporary issues concerning our drinking water, whether sourced from farm wells or supplied by waterworks, is the persistent concern of nitrate contamination. Nitrate infiltrates the soil primarily through the application of fertilizers containing nitrate, leading to elevated nitrate levels in regions with extensive agricultural activities.

Nitrate stems not only from synthetic fertilizers but also from the application of manure and dung onto fields and meadows. Insufficient nitrate in the soil can impede protein production in plants, affecting the quality of crops such as grains. Excessive fertilizer application can lead to plants being unable to absorb nitrate, causing it to enter groundwater or surface waters through runoff during rainfall.

The German Federal Environment Agency reports that approximately 17% of monitoring stations in Germany regularly exceed the groundwater limit values of 50mg/L, with the percentage rising to 27% at monitoring stations with high agricultural use.

Nitrate is present in water, but also in food

A 500kg horse consumes between 20 and 60 liters of water per day, depending on the weather conditions and the horse’s level of activity. Even in the minimum maintenance requirement of 20 liters, it makes a significant difference whether the horse consumes 1g (50mg/L) of nitrate per day or 4g (200mg/L) of nitrate. One gram of nitrate doesn’t sound like much at first. But it doesn’t take much of some substances to cause damage to the body. Dysbiosis (incorrect fermentation) and inflammatory processes in the digestive tract, in particular, are suspected of contributing to an increased conversion of nitrate to nitrite. And such dysbioses are unfortunately very common in our horses.

In horses, the extent to which ingested nitrate is reduced to nitrite has not yet been thoroughly investigated. The more toxic nitrite is produced in the horse’s large intestine. It is transported into the bloodstream through the intestinal wall, inducing the formation of methaemoglobin. Methaemoglobin has a considerably lower binding capacity for oxygen, resulting in oxygen deficiency in the tissues. In acute cases of poisoning, the nitrate/nitrite can lead to colic, diarrhoea, increased salivation, sweating, brown or blue discolouration of the mucous membranes, cramps and other symptoms. In the case of chronic poisoning or overfeeding (which occurs more frequently), the horse is more likely to exhibit a gradual decline in performance.

There are no reference values for nitrate in horses. According to Dietbert Arnold, an expert in horse breeding and keeping, horses react very sensitively to nitrate, and even values of 25-50 mg nitrate/L water can lead to gradual poisoning. Above 50mg/L, acute poisoning can even be triggered. Especially for sport horses or in summer, when water intake is higher than usual due to sweat loss. It is then the straw that breaks the camel’s back.

Because, as everyone can already imagine, the nitrate content in forage crops is also high, especially in areas where the groundwater is already overloaded with nitrate. The more fertiliser is applied, the higher the nitrate content in the plants growing on these areas. The nitrate content in plants varies not only with the amount of fertilizer but also depending on which plants are on the land. In order to produce good haylage, which is not suitable as horse feed due to its high lactic acid bacteria content, the nitrate content in the plant must be high, or additional nitrate must be added via silage additives. Modern high-sugar grasses, especially those with elevated sugar content, exhibit a notable tolerance to nitrate and consequently tend to have a substantially high nitrate content, enabling them to withstand excessive fertilization.

Horse owners can disregard this area as long as it is dedicated to silage production for cows. However, once this area is utilized for horses or if the farmer decides to produce hay from it for sale to horse owners, complications arise swiftly. Carrots and sugar beets, which should be fed to horses in limited quantities or avoided altogether, also exhibit elevated nitrate levels.

Tractor fertilising pasture
Modern high-sugar grasses, specifically, display heightened nitrate tolerance, typically resulting in elevated nitrate content. This trait allows them to withstand over-fertilization.
© Adobe Stock / photoprojektrm

Regular testing is the best protection

You can only impact the nitrate content of the feed by engaging in discussions with your hay supplier about the desired qualities of suitable horse hay. Fortunately, horse hay is typically cultivated more extensively than cattle feed, mitigating the nitrate issues associated with haylage or silage feeding.

However, it is much more important to keep an eye on the nitrate levels in the drinking water. Especially those who supply their horses with well water should have their water analysed at least once a year, more frequently if possible. If you analyze the water in December when you find the time to do so, the quality may be excellent, as agriculture is typically at a standstill during this period. However, if you conduct tests in April, following proper fertilization by the neighboring farmer two weeks earlier, the results may vary significantly. Especially with wells, it’s essential to consider that most of them are not drilled deep enough to tap into true groundwater. Instead, they access water layers closer to the surface, in which inputs from agriculture are directly reflected, from nitrate to coliform bacteria.

Therefore, regularly test stable water, especially well water, to ensure compliance with limit values, particularly concerning nitrate, and overall quality. Initiating an initial comprehensive analysis by sending samples to a certified laboratory is a sensible approach to gaining an overview of the overall water quality.

Nevertheless, due to the considerable seasonal fluctuations in nitrate content in soil water, employing simple test strips for routine checks can provide an approximate assessment of the water’s nitrate levels. Complete swab test sets are available, offering a comprehensive examination of crucial water quality factors, including the pH value, in addition to nitrate levels. Regular testing throughout the year enables the assessment of water quality stability or fluctuations. It helps decide whether using the supply pipe for watering, installing water filters on the well system, or deepening the well would be more beneficial for the horses.