Racehorses are athletes and as trainers, optimum athletic performance is the ultimate goal. Have we discovered all there is to know about unlocking potential? The answer is no. We are still discovering new science in equine physiology all the time, which gives us clues as to how we can use new approaches to improve health and performance in our racehorses.

In recent years, focus has turned towards the emerging science of the Lymphatic System. The Lymphatic system is as important as the well known circulatory system (like the blood vessels), and is fundamental to the functioning of the body and central to the immune system, energy metabolism, detoxification and energy availability in the horse’s body.  A horse with a well functioning lymphatic system can metabolize energy and clear metabolic waste more efficiently, leading to enhanced performance and faster recovery. 

So how do we tap into the benefits of a well functioning lymphatic system? The first step is to understand what it is. Nutrients and oxygen are carried in the bloodstream towards our tissues, but have you ever thought about how they are actually delivered to the cells?

This is where the lymphatic system comes in. The lymphatic system broadly speaking runs in parallel to the circulatory system and creates the point of delivery to the cells and tissues. The circulatory system carries the blood via arteries and vessels which get smaller as they reach the muscle tissue as capillaries, where the wall is only one cell thick.  This enables smaller molecules like nutrients and oxygen to be pushed out of the capillaries, into the fluid around the cells, or lymph, while retaining larger cells like erythrocytes (red blood cells). The lymphatic system is an extensive system of vessels and nodes that transports lymphatic fluid around the body.  There are two main functions of the lymphatic system.

Energy metabolism – transporting nutrients and oxygen to the cells

All the cells and tissues of a horse’s body are surrounded by a watery gel-like substance called interstitial fluid. This provides a medium for dissolved oxygen and nutrients to travel across to the cells. Lymph capillaries, carrying these substances run through the interstitial fluid.  The walls of these capillaries are only one cell thick and have junctions which overlap, making them highly permeable, which allows easy transfer of materials.  In practical terms, this means the horse’s muscles and tissues get all the energy they require to carry out all their metabolic processes. As well as being responsible for giving cells the oxygen and nutrients they need, the interstitial fluid transports salts, hormones, neurotransmitters, co-enzymes, amino acids, sugars and fatty acids around the body via the Lymphatic system.

Detoxification: processing waste products

During the race season, horses are placed under physiological demands and the body has a lot to process. During hard workouts and performance, the body produces a lot of waste products. The thin walled lymph vessels also allow interstitial fluid into them to remove the waste products of cell metabolism (such as cell debris, bacteria, dead blood cells, pathogens, toxins, lactic acid and protein molecules) from each cell. This process is equally important as carrying necessary materials to the tissues to provide energy. These metabolic waste products are carried in the lymph away from the cells for the process of detoxification. Detoxification is the term used for the processes that are happening continuously in the horse’s body to remove waste products, or metabolites that are naturally produced during the body’s normal processes. Detoxification takes place mainly in the liver, kidneys and intestines. For this reason, it is really important to ensure the horse has a healthy and well functioning liver and kidneys. By supporting the liver and kidneys you can help this breakdown process and allow the horse to better metabolize compounds that would otherwise be toxic if they remained in the body.

Gut health is also very important to the lymphatic system and detoxification, given that more than half of the lymphatic vessels of the horse are located within the gastrointestinal tract.  Peristalsis (the natural contraction and relaxation of the gut wall) drives the return of lymph to the rest of the body. Movement in the gut is stimulated by food consumption (mainly long fibers) and is crucial to lymphatic system function as there is very limited muscular contraction in the horses lymphatic vessels themselves. This means it relies on passive forces from movement of other systems in the horse’s body as opposed to active muscle contractions and so feeding continuously around the clock is crucial, not only for maintaining gut health, but to maintain a healthy immune system and detoxification process as well.

Lymphatic System and Immune Function

In addition to lymph and lymph vessels, the horse has around 8000 lymph nodes.  Lymph nodes are bundles of lymphoid tissue and proteins. Lymph nodes act as a filter for foreign substances that travel through the lymphatic fluid, and they contain lymphocytes (white blood cells) that help the body fight infection and disease, and so the lymphatic system is also key to the functioning of the immune system.  As the lymph tissue approaches each lymph node, it slows down and collects in that area.  Due to the fact that horses have so many lymph nodes, they are extremely susceptible to lymph node blockage.  Lymph nodes can actually be felt or sometimes seen at various points around the horse’s body, particularly around the head and neck or when they are swollen.

Horses need to keep moving

Why is movement so important for horses? One very important point to note about the lymphatic system of the horse is that there are no direct muscular contractions within the walls of the lymph vessels to promote the flow of lymph.  This means that the functioning of the whole system relies on the force of movement of other structures in the body, such as the movement of the skin to apply pressure to the underlying tissues to stimulate the transport of lymph through the vessels.

This has particular relevance to the practical care of horses in the modern day, particularly those also stabled for longer periods of time.  It is very common to see leg swelling in these horses, and this has a very simple explanation in terms of the immune system.  This principle of continuous movement being necessary applies especially to the legs of the horse where this elastic movement of the skin is assisted by a pump mechanism in the hoof and fetlock joint.  It is thought that this is the case due to there being no muscles in the lower limbs of the horse to aid the movement of lymph from this area.

Horses therefore need to move extensively and perhaps almost constantly (up to 16 hours per day) to keep the lymph circulating around the body, and standing still for too long significantly impairs the functioning of the lymphatic system.

Practical tips for a healthy lymphatic system

1. Keep horses moving – turn horses out as much as possible  

Horses that are standing still for long periods of time are at risk of an impaired lymphatic system, which can impact the immune system, recovery time and ultimately performance.

2. Cool down for at least 15 minutes after exercise

The period of time immediately after training is important for removal of metabolic waste products – keeping a horse moving after a hard training session stimulates the lymphatic system to continue to remove waste products from cells, which includes the removal of lactic acid. By cooling down properly after every session, you can significantly improve recovery times

3. Consider feeding supplements that can directly benefit the lymphatic system

Functional herbal ingredients in innovative supplements can support lymphatic system function.   Cleavers (Gallium aparine) is known to bring benefits to the lymphatic system. Couch grass (Elymus repens), Nettle (Urtica dioica), and Dandelion (Taraxacum officinale) are all known to have purifying effects which can support metabolism and detoxification.