Happy Gut = Happy Horse

Is your horse nervous, spooky or moody? His diet could be a factor.

Kate Hore RNutr(Animal). R.Anim.Technol., head nutritionist at NAF, looks at the Gut-Brain Axis and its influence on the horse’s behaviour.

If I asked you which organ in your horse’s body was responsible for their behaviour, moods, spooks and spins, you would probably say their brain – and you’d be right, or partly right. The brain, of course, is important but it does not work alone. The role of the digestive tract in behaviour, and particularly its vast microbial population, is

CNS Central Nervous SystemPart of the nervous system, principally the brain and spinal cord.

ENS Enteric Nervous SystemSub-section of the nervous system. A mesh like system of neurons (nerve cells) governing function in the GIT.

GBA Gut-Brain Axis Bi-directional communication between the brain, nervous system and gut.

GIT Gastro-Intestinal TractTotal digestive tract from mouth to rectum well-established along what is called the ‘Gutbrain axis (GBA)’.

The connection between the brain, the gut, behaviour and immunity has long been recognized, and that knowledge continues to grow. It is a complex relationship between the gastrointestinal tract (GIT) and its microbiome, central nervous system (CNS) and enteric nervous system (ENS). Communication along the GBA runs both ways, with changes in the brain able to influence the balance of the microbiome; whilst dysbiosis (imbalance) in the microbes can strongly influence the brain and behaviour. Indeed, human research has shown clear associations between changes in gut microbiota and mental health conditions such as depression and anxiety (Chang et al 2022).

Exact mechanisms controlling this relationship are still not fully understood, but they are known to be complex and likely involving multiple pathways, including neural, endocrine, metabolic and immunological.

Nervous System

The nervous system is integral to the GBA, with roles in the CNS, ENS, and along the Vagus nerve running from the brain to the gut. The Vagus nerve is part of an involuntary nervous system, meaning we can’t consciously control it. Roles for neurotransmitters in both brain and gut are another example of how the nervous system acts directly on the microbiota. Gut microbiome stability influences digestive efficiency and the uptake of nutrients, so impacting endocrine function, which in turn affects the GBA. Meanwhile the role of prebiotics, probiotics and postbiotic metabolites are all being investigated for their potential to stabilise the microbiota, protect the epithelial cell wall of the GIT and positively influence behaviour and mood along the GBA.

Research

The link between digestion and emotions dates back hundreds of years, hence the word ‘gutsy’ meaning brave and determined, but now science is catching up with evidence in horses. The equine hindgut, in particular, is an area of extensive research, and here we discuss just a few recent developments.

The importance of feeding a fibre focused forage-based diet is evident, as research demonstrates the high-starch concentrate diet changes the microbiota, and is seen as increased behavioural reactivity (Bulmer et al 2019). Destrez et al (2019) looked further at responses in horses when exposed to stress from a novelty test and a startle (umbrella) test and how a changed microbiota might influence their reactions. Moving to a lowfibre, high-concentrate diet changed the microbial profile of the hindgut, which was then seen as reactive behaviour during the novelty test, and changed gut chemistry in the startle challenge. Concurrent changes in both behaviour and gut chemistry reflect the bi-directional aspect of the gut-brain axis.

Studying Behaviour

Mach et al (2020) studied a range of variables in a large group of healthy horses kept in similar conditions over eight months, and found two key relationships between health and the microbiota. Firstly behaviour linked to poor welfare, such as stereotypies and aggression, were closely linked to the microbiota, so reinforcing the role of the GBA in horses. Secondly, performance challenges were highly associated with gut microbiota variability. Differences were even seen within discipline, with dressage and jumping recognised as similar to each other, differentiated from horses training for eventing or other specialties. The stressors were recognised less as the training itself, but associated issues such as long-distance transport, stabling and high concentrate diets. Further work from this group has reinforced the link between microbiota and behaviour in horses, and is looking at the benefits of time at pasture for equine athletes, their gut and brain.

When looking at the research overall, a recent scientific review confirms the literature shows evidence of the gut-brain axis and its influence on behaviour in horses. Feeding targeted nutritional support of the microbiota of the GIT is recommended. Ongoing research by Professor Veronique Julliand’s group in France continues to improve our knowledge on the role of probiotics in equine digestion, whilst postbiotic research offers emerging evidence for controlling stress in young horses, and further research – outside the scope of this article – shows evidence for specific nutrients and their role in gastric health.

Maintaining A Stable Gutbrain Axis

• Feed a high fibre, low-cereal diet

• Make changes gradually

• Maximise pasture turnout

• Supplement with targeted support for the microbiome

• Maintain gut wall integrity with evidencebased nutrition

Conclusion

If we go back to that opening question, of ‘Which organ controls behaviour?’, we can see there is clear evidence, both across species and specific to horses, that it isn’t one organ, but a double act between the brain and the gut, along the fascinating corridor known as the Gut-Brain Axis.

Selected References

Full references available on request from info@naf-uk.com

• Bulmer et al (2019) High-starch diets alter equine faecal microbiota and increase behavioural reactivity. Scientific Reports.9; 9(1) 18621

• Chang L et al (2022) Brain-gutmicrobiota axis in depression. Brain research bulletin. 182. 44-56

• Destrez A et al (2019) Dietaryinduced modulation of the hindgut microbioate is related to behavioural responses during stressful events in horses. Physiology & Behavior. (202) 94-100

• Mach N et al (2020) Priming for welfare: gut microbiota is associated with equitation conditions and behavior in horse athletes. Scientific Reports. 10:8311