Your horse’s immune system – why it’s important and how you can boost it

Your horse’s immune system is vital for fighting infections – be it a virus, bacteria, parasite or fungi. Horses with compromised immune function are more susceptible to illness, ill-thrift, and poor performance. So, what can you do to support your horse’s immune system and ensure they stay on top form?

How does my horse’s immune system work and why is it important?

Once a pathogen (e.g. virus or bacteria) has got past the physical barriers designed to keep them out, such as the cough reflex, skin, mucus membranes and mucus itself, your horse’s immune system will spring into action. There are two types of immune response:

Innate immune response – this is present from birth, and acts as the rapid response unit, providing the first line of defence against invading pathogens. The response isn’t specific to the particular pathogen and is referred to as ‘innate immunity’.

Acquired/adaptive immune response – this immunity is acquired throughout life and is referred to as ‘acquired immunity’. It is highly specific, with cells like B cells, which produce antibodies to specific pathogens. If your horse has been exposed to a pathogen before, the cells of the adaptive immune system will recognise it and respond accordingly to defend against it. Vaccination relies on this type of immunity to provide protection. Passive immunity is another form of acquired immunity, and occurs when antibodies are provided to the animal, rather than them making the antibodies themselves. When a foal receives antibodies from the mare’s colostrum, it provides passive immunity

Your horse’s immune system is vital for keeping them alive and healthy – without it, even a mild infection could prove life-threatening. Even slight compromise can lead to recurrent infections, ‘poor-doers’ and suboptimal performance.

What happens if my horse has a low immune system?

The impact a low immune system will have on your horse depends on the severity of compromise. For example, a newborn foal who doesn’t get sufficient colostrum is incredibly vulnerable to infection. Once an infection takes hold, it requires intensive medical care to try and treat, and can often sadly be fatal.

In adult horses, unless there is an underlying genetic or medical problem, the compromise is likely to be milder and so the effect more subtle. Some signs to look out for include:

• Recurrent infections

• Multiple sites of infection (e.g. pneumonia and sinusitis)

• Prolonged treatment times for infections/treatment failure

• Infections with opportunistic pathogens

• Poor performance

• Ill-thriftiness

What can cause my horse to have a low immune system?

There are many potential causes for a weakened immune system in horses:

Genetic problems


• Poor colostrum intake

• Age

• Diet

• Stress

• Underlying medical issues

• Medicines (e.g. steroids)

Genetic problems

Thankfully these are rare but include conditions such as severe combined immunodeficiency (seen in Arabian foals), foal immunodeficiency (Fell pony) syndrome and common variable immunodeficiency. Usually, these are fatal as there is no cure. With the exception of common variable immunodeficiency, which can present later in life, genetic problems usually are apparent in young animals.

Poor colostrum intake

A good intake of colostrum within 12 hours of birth is vital for newborn foals. Unlike some other species they do not receive any antibodies from the mare during pregnancy, so rely on getting these from the colostrum to provide passive acquired immunity (see above). This supports their immunity for the first 6-12 weeks of life until their own immune system starts to develop. When colostrum intake is inadequate it results in ‘failure of passive transfer’ and these foals are highly susceptible to infections.


Young horses have reduced immunity while their immune system is still developing. However, ageing also negatively impacts immune function, resulting in geriatric horses having an increased susceptibility to infections.1


Nutrition plays an important role in immune function. Inadequate vitamin and nutrient intake canlead to a weakened immune system. Non-equine studies have identified Vitamin C, Vitamin D, zinc,selenium, iron and protein as all being vital for the function of immune cells.2


Stress can lead to reduced immune function. This is an important factor in many performance horses as training, transport and competition can all take their toll and be a source of stress.

Underlying medical issues

Hormonal disorders such as Cushing’s disease (pituitary pars intermedia dysfunction – PPID), tumours and viral diseases can all impact immune function.


Some medicines, such as steroids, can reduce immune function. Once the medicine is stopped,immune function usually returns to normal.

How can I boost my horse’s immune system?

There are some steps you can take to help support your horse’s immune function. These include:

• Minimising stress where possible

• Ensuring exercise is within fitness levels

• Maintaining a good body condition

• Feeding a complete and balanced diet, suitable for the level of work

• For foals, a good intake of colostrum is vital

However, sometimes additional support is required to ensure optimal immune function, and this is when supplementing with the key nutrients known to support immunity can be beneficial. For all round daily support, Chevinal is a great choice, as it scientifically formulated for horses, to deliver all the key vitamins, minerals and essential amino acids that they need. For young foals, Friska Foal, multivitamin and prebiotic syrup, will help to support overall health and immune function, particularly during times of stress.

What nutrients are particularly important for good immune function?

Omega oils

Omega oils, and particularly omega-3, are strongly associated with good immune system function – especially the natural anti-inflammatory processes in the body.

Kentucky Karron Oil is a fortified, high quality linseed oil that is readily absorbed, delivering a balanced ratio of Essential Fatty Acids (EFAs), that are essential for healthy immune function.

Vitamin C – long associated with immune health, particularly for the respiratory system, Vitamin C can be made by horses themselves. However, some horses may have a compromised ability to make Vitamin C and would benefit from supplementation. One example is travel stress, with respiratory infection being a particular risk in this scenario. Honey C, with Vitamin C, soothing honey and a blend of herbs renowned for their respiratory health supporting properties can help offer the extra support that these horses need.


Antioxidants are vital for neutralising unstable particles known as free radicals. Free radicals are produced continuously in the body, but can have an impact on cells, if left unchecked. There are many different types of antioxidant – some of which are produced in the body. Some, however, must be obtained from the diet. One example is Vitamin E. Vitamin E works with a trace element called selenium to deliver powerful antioxidant action and support the immune system.

V.S.L is available in a liquid or powdered formulation and contains vitamin E, selenium and lysine – an essential amino acid. Together, these three nutritional components provide antioxidant action and play a vital role in antibody production.

Read more about antioxidants and horses


Often (quite rightly!) associated with coat and hoof health, copper also has essential roles to play in the immune system. Responsible for the correct functioning of various enzymes across the body, deficiencies can negatively impact the immune system. Copper is also important for antioxidant action in the body.

Read more about the importance of copper in horses

Whereas many horses get the copper that they need from their forage, some areas have copper deficient soil, and that deficiency can be passed on to horses. Copper Vit is a copper supplement that is ideal for ongoing use in copper deficient areas. Containing chelated copper for improved bioavailability, Copper Vit is also fortified with manganese, Vitamin E and Vitamin B12, for additional antioxidant and overall health benefits.

To discuss how you can use supplements to help your horse have a strong immune system, why not get in touch with one of our expert team?


1. Hansen S, Baptiste KE, Fjeldborg J, Horohov DW. A review of the equine age-related changes in the immune system: comparisons between human and equine aging, with focus on lung-specific immuneaging. Ageing Res Rev. 2015 Mar;20:11-23. doi: 10.1016/j.arr.2014.12.002. Epub 2014 Dec 9. PMID: 25497559.

2.’s,including%20the%20amino%20acid%20glut amine).

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