Blood Builders in Horses: Do They Work or Cause Harm?

By Dr Duncan Houston

If a horse is underperforming or lacking stamina, blood builders are often suggested. In most cases, they are unnecessary and sometimes harmful.

The idea sounds simple. Increase red blood cells, improve oxygen delivery, and performance should improve. But in horses, the physiology does not work the way many people assume.

This is one of the most misunderstood areas in performance nutrition.

Quick Answer

Most healthy horses do not benefit from blood builder supplements. Iron deficiency is rare, red blood cell levels are naturally regulated, and substances like erythropoietin carry significant health and legal risks. Performance issues are usually caused by fitness, nutrition, or underlying health problems, not a lack of red blood cells.

What Blood Builders Are Supposed to Do

Blood builders aim to increase:

• red blood cell count

• hemoglobin levels

• oxygen delivery to muscles

Common ingredients include:

• iron

• copper

• B vitamins

• folic acid

Some illegal or high-risk approaches involve:

• erythropoietin-like substances

The assumption is that more red blood cells equals better performance.

In practice, this assumption is often incorrect.

Why More Red Blood Cells Do Not Automatically Improve Performance

Horses already have a unique advantage.

They store a large proportion of red blood cells in the spleen.

During exercise:

• the spleen contracts

• red blood cells are released into circulation

• oxygen-carrying capacity increases naturally

This means:

• a resting blood test does not reflect performance capacity

• many horses already have sufficient red blood cells during work

In practice, the system is already optimised for performance.

Why Iron Supplementation Is Usually Unnecessary

Iron is one of the most over-supplemented nutrients in horses.

Key points:

• true iron deficiency is rare

• most diets already provide adequate levels

• the body tightly regulates iron absorption

Excess iron:

• does not improve performance

• may interfere with other minerals

• can contribute to oxidative stress

In practice, adding iron without a confirmed deficiency offers no benefit.

The Problem With “Low Red Blood Cell” Results

This is a common misunderstanding.

A horse may show:

• lower red blood cell count at rest

This does not mean:

• anemia

• deficiency

• reduced performance potential

Because:

• a large portion of red blood cells are stored in the spleen

• they are released during exercise

Treating a resting number without context is one of the most common mistakes.

The Risks of Erythropoietin and Similar Substances

Erythropoietin, or EPO, is sometimes misused to artificially increase red blood cell production.

This is dangerous.

Known risks include:

• thickened blood

• increased risk of clotting

• cardiovascular strain

• potential for sudden collapse

There are also:

• immune system complications

• regulatory and legal consequences

In competitive settings, these substances are prohibited.

How Serious Is This?

Low Risk Situation

• balanced diet

• no supplementation

• normal performance

What this means: no intervention needed

Moderate Concern

• use of over-the-counter blood builders

• no confirmed deficiency

What this means: unnecessary supplementation

High Risk

• high-dose iron supplementation

• multiple combined products

What this means: potential metabolic imbalance

Critical

• use of EPO or similar substances

• signs of cardiovascular stress

What this means: serious health risk

When Blood Support Is Actually Needed

There are legitimate cases where support is required.

These include:

• confirmed anemia

• blood loss

• chronic disease

• recovery from illness or surgery

In these situations:

• treatment should be targeted

• diagnosis should guide therapy

This is very different from routine supplementation.

What To Do If Your Horse Lacks Performance

Instead of reaching for blood builders, assess:

• overall fitness level

• feeding program

• forage quality

• electrolyte balance

• hydration

• underlying health issues

In practice, performance issues are far more often linked to these factors.

Common Mistakes

• assuming fatigue equals anemia

• supplementing iron without testing

• misinterpreting blood results

• using multiple overlapping products

• chasing performance gains through supplements instead of management

These are some of the most common patterns seen in performance horses.

Long-Term Approach to Performance

The most reliable way to improve performance includes:

• structured conditioning

• balanced nutrition

• appropriate workload

• good recovery practices

There are no shortcuts that replace these fundamentals.

Frequently Asked Questions

Do blood builders improve performance?
Not in healthy horses. There is no consistent evidence of benefit.

Is iron deficiency common in horses?
No. It is rare and should be confirmed before treatment.

Why do blood tests sometimes look low?
Because many red blood cells are stored in the spleen and not circulating at rest.

Is EPO safe in horses?
No. It carries serious health risks and is prohibited in competition.

When should I consider blood support?
Only when a true deficiency or medical condition has been diagnosed.

Final Thoughts

Blood builders are a classic example of a concept that sounds logical but does not hold up in practice.

The key points are:

• most horses already have adequate red blood cell capacity

• supplementation rarely improves performance

• excessive or inappropriate use can cause harm

The better question is not how to increase red blood cells, but whether the horse’s overall management supports performance.

If you are unsure whether your horse truly needs supplementation or want help reviewing performance, nutrition, and health factors together, ASK A VET™ can guide you with clear, practical advice tailored to your horse.