Hindgut & Its Importance to the Horse

I came across this article while perusing the internet in my on-going search for information about the hindgut and its importance to the horse. Dr. Beech was kind enough to authorize me to republish this on our site. 

Originally Published April 3rd, 2021

Spring Grass and Performance Issues

With the weather finally improving, lush spring grass is appearing in our fields. It is important to manage this new growth closely as it can not only lead to colic and laminitis but also can cause tension and reduced performance. It is this latter issue relating to performance that we will be discussing in this article.

************************************************

At this time of year, a lot of the cases that I see have one thing in common…….a hind end tension. It can be displayed in many ways.

The symptoms can include:

• Lumbar muscle tension 
• Stiff hind end
• Flank sensitivity
• Girthiness
• Canter issues (often left canter)
• Pushing saddle to left
• Trot to canter transition issues
• Toe dragging
• Reduced propulsion from behind
• Not “tracking up”
• Hindleg limb flight towards midline of body (medial)
• Unhappy with farrier lifting hind limbs
• Kicking out/bucking
• Overly hormonal seasons
• Tension in right side of poll

Why is this?

There are multiple factors involved in the performance issues above. Most center around the involvement of the hindgut.  

Gut environment (bacteria and acid)

Horses are hindgut fermenters. They have a large hindgut that is used to break down all the fibers in their diet. The main area for this digestion is in the caecum (located on the right flank of the horse). The caecum is a 30-45 litre vat which is full of special bacteria that can digest the fibre (cellulose) in the horse’s diet and turn it into absorbable products.

The sugars in the lush grass create an acidity in the hindgut as they are digested by the bacteria. This change in acidity (lowering pH) upsets the delicate bacterial balance in the gut which can lead to bloating, upset/sensitive tummy, diarrhea/constipation (IBS). 

Organ-spine link

However, the issue does not stop there….importantly there is a strong neurological relationship between the spine and the organs. This neurological relationship is based on a viscero-sensoric link. The organs are supplied by nerves from certain portions of the spine. Irritation of the organs causes irritation of the related spinal cord sections which in turn leads to local muscular tension as the spinal nerves also innervate the surrounding muscles. 

This relationship goes both ways. An organ issue will reduce the mobility of the section of spine linked to it but if you have reduced mobility of the spine you can have organ issues as a result. It is why people with IBS have tight backs and why people who have tight backs are more likely to have IBS.  

So horses who already have back tension are far more susceptible to these changes and those with an upset gut can have tight backs…

Why the right hind?

The involvement of the caecum which is located on the right flank is why there are more issues on the horse’s right hand side. It is the right hand that often has increased tension/reduced mobility and why we have the symptoms listed above.

Fascial tension

Another contributing factor is that the increased acidity (acidosis) of the hindgut causes increased contraction of the fascia. This leads to local tension and even whole body tension as it spreads. The horse feels generally tight with increased tone and reduced mobility.

This increased, often unilateral tension can put abnormal strain on certain limbs (often right hind) which can produce an unsoundness. This may present as a lameness but care should be taken as to whether that unsoundness is due to a genuine lameness on that limb or is it just a symptom of the tension due to the hindgut. It may well be that addressing the hindgut removes that unsoundness and therefore the need for veterinary investigation. 

What can be done?

• Manage the grass: This may involve restricting turn out to limit the time in front of the new spring grass. Supplementing with hay is often useful.
• Supplement the hind gut: Hind gut supplements can be used in conjunction with tight management of the grass. Good herbal supplements along with buffers can be given to assist the hind gut. (Hind gut buffers should not be confused with gastric/stomach supplements). I also like to give milk thistle to keep the liver tip top during the spring grass onslaught. Pro and prebiotics are helpful too.
• Mobility: Maintaining spinal mobility is important as those horses with a tight spine are more likely to get gut issues. Mobility can be maintained through bodywork but also through correct exercises both in-hand and ridden.
• Testing: The hind gut can be monitored with fecal blood tests, checking fecal pH and also looking at the bacterial population through fecal sampling.

As ever if your horse is showing signs of performance issues it is always important to evaluate the WHOLE HORSE to ensure that all factors are considered.