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Even if you have successfully obtained high-quality hay, its condition often deteriorates due to the predominantly warm winters in many barns, despite optimal storage conditions. Whenever hay is dried on the ground, mould always gets into the dried material within 50 hours.

This means that it is virtually impossible to find hay completely free of mould. However, the horses are not bothered by small amounts of it.

Even in nature, particularly during winter, forage may not always be of optimal quality in terms of microorganism population. As a result of evolution, horses have developed mechanisms to cope with a certain level of mould in their forage. However, warm and humid winters create ideal conditions for excessive mould growth in hay. Consequently, it is now possible that bales of hay, which were initially of excellent and perfectly dry quality when harvested last summer, may appear dusty and musty upon opening, indicating a clear presence of excessive mould.

Mould infestation is not always visible at first glance

These bales may appear completely normal on the outside, and it is only upon opening them that the extent of the problem becomes evident. The mould can permeate the bale from the inside out, rendering it visibly mouldy. Bales that were stored at the bottom, absorbing moisture from the ground, or those against walls that experienced condensation or were exposed to the elements in draughty barns, are particularly susceptible to mould infestation.

In such cases, the grey, clumped boards on the outside of the bale are a clear indication of mould presence. However, this is often just the tip of the iceberg, as the entire bale is usually affected due to prolonged storage time.

In normal circumstances, these spoiled bales would be discarded and replaced with hay of better hygienic quality. Unfortunately, due to significant harvest losses in recent years, finding hay of suitable quality is a challenge, if not impossible. Even when hay is available, it often falls short in terms of quality compared to what is stored in one’s own barn.

The first farmers may have harvested hay early in the year, but hay cut from late May or early June is richer in nutrients and not ideal for leisure horses or those prone to metabolic issues.

Hay storage has an influence on quality

In addition, hay needs to “sweat” for at least 8, preferably 12 weeks after harvesting. During this time, toxins from plants like buttercups or endophytes are broken down, and digestibility improves. Feeding hay too early can lead to severe health issues such as laminitis or colic. Therefore, hay from the current year should not be fed until autumn at the earliest.

© Adobe Stock/abriendomundo

Leaving horses on pastures for 24 hours is not always the ideal solution either. It requires sufficiently large areas for the horses to find enough feed (approximately 1-2 hectares per horse), and not every horse should have prolonged access to pastures due to variations in metabolism and the quality of the feed available in the meadows.

Minimising problems

To address these challenges, many stables have no choice but to rely on last year’s hay to sustain the horses until the new harvest can be fed. To minimize the risk of respiratory issues caused by airborne mould spores, it is possible to moisten the hay.

Simply using a watering can to distribute water over the hay, ensuring it becomes damp, is often sufficient. Alternatively, a flower sprayer with a large water container, pressurized by a manual pump, can be used to spray the hay evenly. (These can be found at any garden center and are commonly used by garden owners for applying pesticides. It is important to use new, unused, and thoroughly cleaned equipment.) This method has proven to be effective.

The sprayer emits a fine mist of water that forms a moist film over the hay, binding the spore dust without saturating the hay, which could lead to fermentation processes at high temperatures. Dunking the hay is not recommended as it is not only a labor-intensive task but also causes stress to the mould in the hay, resulting in increased spore release. Additionally, soaked hay tends to ferment quickly in warm weather, requiring multiple small portions to be given throughout the day. If the hay racks are only filled once or twice daily, the hay the horses have to consume is often unappetising.

This can be more burdensome for the respiratory tract and metabolism than if the hay had been lightly moistened.

Mould fungi

In cases where there are already horses in the stable with respiratory allergies that react to mould spores with coughing or asthma (heaves), simply moistening the hay is often not enough – the mould needs to be eliminated.

Hay steamers, which can be purchased commercially or built using available construction guides on the internet, are great for this purpose.

Moistening or steaming can effectively address the issue of respiratory exposure. It is important to note that the mould itself cannot colonize the horse’s intestines.

Mold requires oxygen to survive, which is scarce in the horse’s digestive system. Therefore, mould is only transported through the system and excreted with the feces. However, the mycotoxins (mould toxins) produced by mould are problematic as they are not reduced by moistening, soaking, or steaming.

There are a considerable number of mycotoxins that are absorbed through the intestinal wall and pose a significant burden on the horse’s detoxification systems. Some of them also have a detrimental effect on the horse’s large intestine flora, potentially leading to dysbiosis (impaired fermentation).

Mycotoxin binders

However, these mycotoxins can be effectively bound using commercial mycotoxin binders like Okapi’s EndoProtect. The efficacy of mycotoxin binders has been proven through numerous in vitro and in vivo studies. These binders are cell wall proteins derived from specially bred yeast strains, capable of binding various types of mold toxins.

© Okapi GmbH

Once bound, these toxins remain in the food bolus and are subsequently excreted in the faeces. To produce mycotoxin binders, the yeast is “shredded” after the multiplication phase to release the cell wall proteins.The resulting mixture is then dried and typically combined with specialized rock meals such as bentonite before being offered as feed. Horses generally consume these mycotoxin binders without any issues.

They can be sprinkled over moistened hay for the entire group or, if not everyone wishes to share the cost, added to the feed or a handful of soaked hay cobs.

However, it is important to note that this does not justify providing horses with moldy feed as a general practice. Even with the best management, mould places an increased strain on the organism.

Nevertheless, these mycotoxin binders can help bridge the gap until new, hygienic hay becomes available, allowing for a switch back to healthier feed. And then it’s time to finally throw the old mouldy bales on the muck heap.

More on hay quality and storage: The basics in storing hay