The Hindgut Microbiome and Behaviour – what’s the connection?
Most of us are aware there is often a link between a horse’s diet and their behaviour, but were you aware of the impact of their hindgut on behaviour? Whilst the link between the central nervous system (CNS) and intestinal tract helps explain how diet affects behaviour – with horses fed certain diets sometimes becoming more reactive – and how the brain (and mental health) affects gastrointestinal (GI) tract function, recent research has taken this relationship one step further, adding the hindgut microbiome to the mix, creating a complex system called the microbiome-gut-brain axis (MGBA).
In our latest Technical Blog, Lisa Elliott. MSc, Equine Nutrition Solutions, breaks down the complex relationship between the nervous system (brain), digestive tract, and the hindgut microbe population, how the hindgut microbiome can affect behaviour, and how to ensure you are feeding the right diet to minimise reactiveness and promote calmer behaviour:
The Hindgut Microbiome
Your horse’s hindgut is home to billions of microbes, known collectively as the hindgut microbiome, who breakdown fibre through a process called fermentation, and convert it into a usable energy source as Volatile fatty Acids (VFA). These microbes include bacteria, who are predominately responsible for fibre fermentation, but also Protozoa, Archaea, and fungi.
Alongside fibre fermentation and the production of VFAs the hindgut microbiome also produces other compounds or ‘metabolites’ which can enter the bloodstream from the hindgut. These metabolites can influence several physiological functions and organ systems, including the brain. The hindgut microbiome also has a significant impact on your horse’s immunity and overall health and well-being.
Changes in the balance of microbes and resulting microbial dysbiosis often associated with certain diets or abrupt dietary change can lead to metabolic disorders, gastrointestinal diseases, and neurologic conditions. A healthy, diverse, and balanced microbiome which promotes a healthy hindgut, is therefore, essential for optimum mental and physical health.
The Microbiome–Gut–Brain Axis (MGBA)
It is well known that there is a two-way communication system between the horse’s gut and their brain, referred to as the gut-brain axis, which means your horse’s gut can have a significant impact on their overall mood and behaviour. Research has confirmed the link between the hindgut microbiome and an individual’s health and wellbeing, and there is a growing body of scientific evidence that hindgut microbes can influence communication between the gut and the brain directly. This communication system has several routes (or pathways), some of which involve direct communication via the nervous system and others that involve indirect communication through the neuroendocrine and immune systems. All these pathways by which the gut and brain communicate are thought to work together. This means that neural, neuroendocrine, and immunological signals allow the gut (including the microbiome) and brain to communicate with one another in a complex, bidirectional fashion.
There is evidence that the microbial populations that live in the gut play a key role in influencing the gut-brain communications, which has led to the concept of the microbiome-gut-brain axis (MGBA). The influence of the microbes in the gut is thought to impact on the central nervous system and thus influence behaviour. Metabolites produced by the microbiota also affect brain function by influencing the physiology of the endocrine and immune systems. Basic functions regulated by the gut microbiota through the gut-brain axis include intestinal motility, secretions, permeability, and mucosal immunity.
Although it is not yet fully understood how microbiota in the gut impact on behaviour, it is thought that one of the pathways is via the vagus nerve. The gastrointestinal tract is heavily innervated by the vagus nerve, which serves as a direct communication channel to the central nervous system. However, it is thought that the communication extends to other pathways as well; for example, research has shown an association between behaviour and immune response.
Studies have also shown links between gut microbiota and early behavioural development (Homer et al. 2023). For example, a disrupted, less established microbiome has been shown to influence the development of cognitive and behavioural disorders and promote a greater response to stress in young animals compared to those with a well-established, balanced microbiome. Whilst it’s not entirely clear why this occurs, one possible explanation is through hormones produced by the gut microbes. The gut microbes can produce specific hormones that function as chemical messengers or ‘neurotransmitters ‘between the gut and the brain, including serotonin and dopamine. These neurotransmitters are involved in several physiological functions, including locomotion, gut motility, as well as having a significant role in behavioural responses.
Research has shown that levels of neurotransmitters can be regulated by gut microbiota (Kennedy et al. 2017) with certain bacteria shown to increase the levels of the amino-acid tryptophan, which is involved in the synthesis of serotonin, which is known to improve mood and reduce anxiety. In fact, the addition of certain bacteria into the gut have been shown to be more effective in the treatment of depression and anxiety than pharmaceutical drugs (Yang et al. 2019; Bibbo et al. 2022).
How the Hindgut Microbiome affects Behaviour
Any disturbance to the balance of hindgut microbes and the growth of less desirable microbes can result in behavioural changes. Recent research (Destrez et al. 2015; Bulmer et al. 2015; Bulmer et al. 2019) has shown that horses receiving higher starch diets had higher heart rates and were far more reactive and nervous than those on higher fibre diets, which was attributed to changes in the gut microbiome from the higher starch diet. Significant differences in bacterial communities were also seen between those on the higher starch and high fibre diets. Animals fed the higher starch diet had increased levels of amylolytic (starch degrading) bacteria, notably Streptococcus species which produce lactic acid, and a reduction of fibre digesting bacteria like Ruminococcaceae.
In humans Firmicutes, which are a group of bacteria with a significant presence in the equine hindgut, have been shown to influence the production of serotonin by reducing the availability of tryptophan. Therefore, it is possible that conditions such as dietary change or higher levels of starch reaching the hindgut, which result in alternations in bacterial populations, may lead to a reduction in serotonin production, which has been seen in other species. Simply put, an increase in less desirable bacteria associated with higher starch diets and a decrease of beneficial fibre digesting bacteria, can affect the levels of neurotransmitters like serotonin and dopamine created in the gut, which then in turn can mean the horse becomes more stressed, reactive, and tense.
Additionally, studies have also shown a link between reduced microbial species diversity in the gut and the development of abnormal behaviour across many animal species, including horses (Homer et al. 2023).
Supporting Calmer Behaviour through a Healthy Hindgut Microbiome
A healthy and diverse hindgut microbiome is associated with reduced stress responses, improved learning, and enhanced overall well-being. So, to promote calmer behaviour and optimise mental well-being, you need to maintain a happy, healthy microbiome through the right diet and nutrition:
Low starch and High Fibre
It is interesting to note that the amount of starch fed in research studies, was less than many leisure horses receive in their daily feed, which shows that even small amounts of starch in the diet can have a significant effect on a horse’s behaviour. Therefore, providing a high fibre, low starch diet is essential to maintain a healthy hindgut microbe population and help minimise tense, reactive behaviour in your horse or pony.
Fibre in the form of forage such as hay and grasses should always form the foundation of your horse’s diet, and a constant supply is essential to promote both microbial and hindgut health. Hindgut microbes thrive on plenty of complex forage to break down through fermentation, producing slow-release energy which helps to maintain calmness. Ad-lib forage keeps the microbes in your horse’s gut happy and healthy, promoting microbial equilibrium and creating the right conditions in the hindgut to facilitate the growth of beneficial fibre-digesting bacteria. Volatile Fatty Acids produced by fibre-digesting bacteria in the hindgut also help regulate the stress response by attenuating cortisol – which is linked to more reactive behaviour. Maintaining the right balance of hindgut microbes by feeding of plenty of forage will, therefore, help reduce the potential for stress or anxiety and encourage a less reactive approach in your horse.
Additionally, you can help promote a more diverse microbiome through feeding mixed species hay or grazing and feeding a variety of forages, for example, grass, hay and haylage. Hedgerows are often a haven for mixed, native species and will provide plenty of diverse forage. So, letting your horse graze them or taking them for a wander to browse the hedgerow is ideal to help increase microbial diversity in the hindgut.
If your horse needs more energy to support harder work, it is always better to provide this through sources of highly digestible fibre like Coligone Fibre Cubes or Coligone Fibre Pro as opposed to starch from cereals. Feeding additional fibre like this will also further promote increased microbial diversity.
Probiotics and Prebiotics
Probiotics are thought to promote microbial health by introducing certain live microbes to improve and support the hindgut microbe population. Yeasts such as Yea-sacc, have also been shown to stimulate and nurture fibre fermenting bacteria and increase fibre digestibility.
Prebiotics work differently to probiotics in that they provide a food source for beneficial bacteria and help to encourage their growth and decrease the growth of less desirable bacteria. ScFOS prebiotics provide food for beneficial bacteria and several studies have shown that ScFOS can help mitigate disruptions to the hindgut microbes and restore a healthy equilibrium. MOS works in a slightly different way to ScFOS but can bind to invading or increasing pathogenic microbes and take them out of the hindgut, helping to encourage growth of beneficial microbes and promote a healthy, balanced microbiome.
All three of these important pro and prebiotics are included within Coligone Power and Liquid and the Coligone Balancer range, which can be fed alongside a forage and fibre-based diet to provide optimum nutritional support for a healthy, balanced hindgut microbiome and help your horse to stay calm and focused in all situations.
If you have any questions about creating the best diet for your horse and keeping your horse healthy through the right nutrition, please contact Coligone – 0333 0503785/07986 183616 or sales@hbradshaws.co.uk.
