When the immune system becomes overactivated – why yeast in horse feed can do more harm than good

Do you want a horse that will last for many years – or one that burns out far too quickly?

Imagine a sport horse that is always a little sore after training, recovers slowly and regularly gets minor injuries. Many people first think about shoes, saddle or training plan – but forget about the feed. What if the problem starts with an immune system that is constantly working overtime?

What does yeast do in the body?

Feed yeast (e.g. Saccharomyces cerevisiae ) is often used in feed mixtures, mash and supplements. It contains, among other things, β-glucans , which activate immune cells in the intestine (Perricone et al., 2022).

• In the short term : Can help if the horse is sick, under antibiotic treatment or under heavy stress.

• Long term : Constant immune activation can create imbalance.

When the immune system “works overtime”

An immune system needs to be ready to act – not on alert all the time. If it is overactivated, it can cause:

• 🔻 Energy loss : Immune reactions require energy that the horse could otherwise use on muscles, performance and recovery.

• 🔻 Low-grade inflammation : Constant activation can strain mucous membranes, joints and muscles.

• 🔻 More recovery time : Importance for training plan, performance and durability.

• 🔻 Increased risk of injuries and pain : More vet visits and a life marked by minor problems.

In research with both horses and other animals, this very link between yeast, immune response and increased inflammation load is seen (Lucassen et al., 2022; Liu et al., 2024).

So why is yeast used in feed?

In slaughter animals such as cattle, pigs and poultry, yeast is used almost consistently because the goal is rapid growth and efficient feed utilization .

• This gives better weight per kg of feed.

• Immune activation makes animals more robust in short production cycles.

👉 But riding and sport horses are not animals for slaughter. It's about long-term health, stable joints and durable muscles – not short-term weight gain.

Balance vs. Overactivation

• Balance

  • Energy for muscles

  • Calm recovery

  • Healthy joint tissue

  • Stable well-being

• Overactivation (e.g. adding yeast daily)

  • Energy for immune response

  • Slow recovery

  • Increased inflammation in joints/muscles

  • More injuries and vet visits

Regulator Complete's choice – calm and durability over overactivation

At Regulator Complete, we believe that calmness, stability and natural balance provide the best base for a horse that will last for many years.

That's why we choose not to add yeast to our products. Instead, we work with:

• Natural fibers that fill the intestines without overstimulating them.

• Balanced amounts of protein and amino acids that build strong muscles.

• Omega-3 fatty acids, which naturally reduce inflammation.

It provides a body in balance – ready to perform, recover and live a healthy life without unnecessary pain.

Sources

• Perricone V. et al. (2022). The Role of Yeast Saccharomyces cerevisiae in Supporting Gut Health in Horses: An Updated Review… Animals . PMC9774806

• Lucassen A. et al. (2022). Saccharomyces cerevisiae fermentation product and the equine gut microbiome . Animals .

• Liu X. et al. (2024). Yeast peptides in calves: immune and anti-inflammatory effects . Front. Know. Sci.

• Yi S. et al. (2025). Effects of Yeast Cultures on Growth Performance, Fiber Digestibility, Health of Beef Cattle . Animals .

• Pang Y. et al. (2022). Yeast Probiotic and Yeast Products in Enhancing Livestock . J. Fungi .

⚖️ Note: This article is based on published research on yeast in animal nutrition. It is written for general information and does not replace individual advice from a veterinarian or feed expert.