A healthy immune system starts with a healthy gut. In horses, the hindgut plays a key role in digestion, fibre fermentation and immune function. The immune system has co-evolved along with the hindgut to create defences against pathogens. The importance of this interaction is clearly highlighted by the fact that 70–80% of the body’s immune cells are found in the hindgut. 

Hartog Digest has been developed to support both digestive and immune function. Thanks to the combination of prebiotics and scientifically proven TruEquine™ postbiotics, Hartog Digest helps support a healthy hindgut environment, a balanced microbiome and resilience during periods of stress. 

The link between the hindgut and the immune system 

The immune system protects the horse by recognising and responding to potential threats. It consists of cells and molecules that work together to help maintain health, support recovery and protect the body against unwanted challenges. 

The digestive system and immune system are closely connected. This is especially true in the hindgut, where the caecum and colon are located. These organs are home to a large part of the horse’s microbiota: the community of bacteria, yeasts and other microorganisms that live in the digestive tract. 

A healthy hindgut supports more than digestion alone. It also plays an important role in maintaining gut integrity, supporting the immune system. 

Why the hindgut is so important for horses 

Horses are hindgut fermenters. This means they rely on microorganisms in the hindgut to break down fibre from forage such as hay, grass and lucerne. 

During this fermentation process, beneficial microbes produce volatile fatty acids, also known as VFAs. These VFAs are absorbed by the horse and used as an important source of energy. 

VFAs also help support: 

• a healthier hindgut environment; 
• hindgut resilience; 
• hindgut absorption;
• cell growth; 
• blood flow; 
• functioning of the intestine; 

When the hindgut functions well, the horse is better able to use fibre efficiently and maintain digestive balance. 

How Hartog Digest supports VFA production 

Hartog Digest contains TruEquine™ postbiotics. These postbiotics are produced through a controlled fermentation process and provide beneficial fermentation metabolites directly. 

Scientific studies have shown that horses fed the postbiotic used in Hartog Digest had a higher concentration of VFA production compared to horses only fed inulin, a prebiotic fibre. (source TruEquine™). 

This is important because VFAs are one of the key results of healthy fibre fermentation. By supporting VFA production, Hartog Digest helps support the hindgut environment, digestive function and the natural connection between gut health and immune function. 

Want to learn more about the differences between prebiotics, probiotics, and postbiotics? You can read about it here.

Innate and adaptive immunity: what is the difference? 

The immune system has two main components: innate immunity and adaptive immunity. 

Both are important for keeping the horse healthy, but they work in different ways. 

Innate immunity: the first line of defence 

Innate immunity is the horse’s first line of defence. It responds quickly and non-specifically to potential threats. This part of the immune system includes physical barriers, like skin, immune cells and inflammatory responses, which are present from birth. 

The postbiotics in Hartog Digest help support innate immunity by activating natural killer cells and helping regulate the inflammatory response according to the size of the challenge. 

This means the immune system is supported in responding effectively, without overreacting unnecessarily. (source: better together maintain immune strength and promote digestive health to help horses feel and perform their best) 

Adaptive immunity: a targeted immune response 

Adaptive immunity is slower, but more specific. It develops over time and recognises particular pathogens. This part of the immune system is responsible for producing antibodies and creating memory cells that help protect the body against future exposure to the same threat. 

The postbiotics in Hartog Digest help support adaptive immunity by contributing to mucosal barrier protection, immune function and recovery. 

A healthy mucosal barrier is important because it helps protect the intestinal wall and supports the horse’s natural defence system from within. (source: better together maintain immune strength and promote digestive health to help horses feel and perform their best)

Why gut health matters during stress 

Stress can affect the horse’s digestive system and immune balance. Situations such as transport, competitions, veterinary visits, moving stables, seasonal changes or ration changes can place extra pressure on the horse. 

During these moments, the hindgut and immune system may benefit from additional nutritional support. 

Hartog Digest helps support the digestive system during stressful periods by supporting: 

• Provides a consistent supply of metabolites and fermentable nutrients  

• Stimulates the production of volatile fatty acids (VFAs) in the hindgut  

• Supports healthy gut function during periods of stress  

• Contributes to a stable and diverse gut microbiota 

This makes Hartog Digest a practical choice for horses that need extra support during periods of change, pressure or sensitive digestion. 

70–80% of the body’s immune cells are found in the hindgut. Stress can affect the horse’s digestive system and therefore immune response. 

Hartog Digest: supporting immunity through the gut 

Hartog Digest supports the immune system by supporting the gut. 

Its formula combines prebiotics and postbiotics to help nourish the microbiome, support hindgut health and provide valuable fermentation metabolites directly. 

This makes Hartog Digest especially suitable for horses that need digestive and immune support, such as horses with sensitive digestion, horses in training, competition horses or horses going through stressful periods. 

By supporting the hindgut, microbiome and therefore immune function, Hartog Digest helps your horse stay resilient and ready to perform. 

Frequently asked questions about gut health and immune support in horses 

How does the hindgut support the immune system in horses? 

The hindgut is closely connected to the immune system. 70–80% of the body’s immune cells are found in the hindgut. Hartog Digest supports the immune system through activation of natural killer cells, supporting the mucosal barrier and regulating the immune response. 

What are VFAs and why are they important for horses? 

VFAs, or volatile fatty acids, are produced when beneficial microbes ferment fibre in the hindgut. They are the horse’s main source of energy and play an important role in supporting gut health, nutrient absorption and overall digestive balance. 

How does Hartog Digest support the immune system? 

Hartog Digest supports the immune system by supporting the gut. Its TruEquine™ postbiotics help support innate and adaptive immunity, gut barrier function, microbial balance and VFA production. 

What is the role of postbiotics in immune support? 

Postbiotics provide beneficial fermentation metabolites directly. These metabolites help support a healthy gut environment, intestinal function and immune function without relying on live bacteria surviving passage through the digestive tract. 

Is Hartog Digest useful during stress? 

Yes. Hartog Digest can be useful during periods of stress such as transport, competitions, veterinary visits, stable changes, seasonal transitions or ration changes. These situations can affect digestive balance, and Hartog Digest supports a healthy hindgut microbiome for optimal gut health, digestion,and function 

Why does Hartog Digest contain TruEquine™? 

Hartog Digest contains TruEquine™ because this postbiotic technology supports both digestive- and immune function. Its effectiveness has been proven in 17 scientific equine studies.