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The immune system is a complex network composed of various components, each with its specific role.

Among these, the intestine stands out as a pivotal player in immune function. Its extensive surface area exposes it to potential pathogens entering the body through food.

In horses, about 80% of immune cells reside near the intestine, constituting what is known as the gut-associated immune system.

Connection between intestine and immune system

This immune system surrounding the gut, often referred to as the gut-associated immune system, not only actively prevents pathogens from entering via the intestine, but also engages in an intricate interaction with the microbiome—the bacterial colonisation within the gut. Any disruption to this interaction, such as dysbiosis (imbalanced fermentation) in the large intestine, can contribute to various ailments including allergies (like sweet itch or “hay allergy”), metabolic syndrome, inflammatory conditions (like osteoarthritis), and even cancer (such as melanoma).

The microbiome significantly influences the efficiency of the immune system. Disruptions to the microbiome can compromise the immune system and lead to the development of diseases.

Influence of feeding on the microbiome

The interplay between the microbiome and immune system is influenced by various factors, with feeding practices playing a central role. Abrupt feed changes, sudden introduction of new mixed feeds, and even the feeding of pro- or prebiotics can have negative impacts on the microbiome. Antibiotics and frequent deworming also affect the microbiome’s composition. It’s important to avoid unnecessary antibiotic use and adopt selective deworming practices to minimise such disturbances.

While researchers are still exploring the optimal composition of the microbiome in horses, some conclusions have been drawn. There is no such thing as a universal and optimal gut flora, whether for horses or humans. Each living being possesses a unique and personally tailored arrangement of microorganisms within their digestive tract. Moreover, this composition is susceptible to transformation throughout one’s lifespan. An additional confirmed observation is that heightened microbial diversity correlates with enhanced intestinal well-being. Conversely, any factor that results in a reduction of the assortment of microorganisms residing in the gut can impose stress on the immune system.

Equine immune system
© Nadine Haase / Adobe Stock

Pro- and prebiotics can disturb the intestinal balance

Pro- and prebiotics, like brewer’s yeast or lactic acid bacteria, should be avoided in horse feeding. They are unnecessary for the digestion of fibre-rich foods and their inclusion can disrupt the balance of the gut microbiota.

To restore the optimal gut flora, emphasising the feeding of high-quality, low-sugar hay is essential. Hay contains abundant cellulose, a plant fibre that serves as a key prebiotic in equine nutrition. During the breakdown of cellulose-rich food, short-chain fatty acids are released, imparting an immune-boosting effect and preserving the integrity of the intestinal lining. This process fosters the growth of vital digestion-supporting bacteria while inhibiting the proliferation of others.

A healthy gut is crucial for a strong immune system!

Particularly for horses dealing with recurrent infections, delayed wound healing, or susceptibility to allergies, there’s a desire to fortify the immune system. The feed industry offers an array of products ranging from echinacea to zinc, all aimed at achieving this goal. Nevertheless, insights from numerous studies highlight that the most effective approach to boosting the immune system is to allow it to function without undue interference. Minimising additional stress and burdens optimises its performance—resulting in reduced inflammation, mitigated allergies, and enhanced swift and efficient response to invading pathogens. Central to this process is the health of the large intestine. Therefore, the ultimate objective of immune system support revolves around fostering a wholesome foundational diet with ad lib access to hay, maintaining a low-stress environment, and fostering the stability of the innate microbiome.