PRP, IRAP or Stem Cells? Choosing the Right Biologic for Equine Osteoarthritis

Biologics are everywhere—but which one to choose? 

Regenerative medicine has transformed equine orthopaedics over the past decade. Today, platelet-rich plasma (PRP), interleukin-1 receptor antagonist protein (IRAP), and mesenchymal stem cells (MSCs) are frequently discussed as alternatives or adjuncts to conventional osteoarthritis treatments¹. 

The challenge for practising veterinarians is not finding these therapies—it is determining when they are truly justified. 

Why Biologics Gained Popularity 

Traditional OA therapies primarily target symptoms. Biologic therapies, on the other hand, aim to influence the inflammatory environment within the joint and support tissue repair processes. 

Although none of these therapies can currently be classified as disease-modifying osteoarthritis drugs (DMOADs), they offer new possibilities for managing difficult cases¹. 

PRP: The Most Accessible Orthobiologic 

PRP is produced by concentrating platelets from the horse's own blood. These platelets release growth factors and anti-inflammatory mediators that may support healing and modulate inflammation². 

Advantages 

• Easy to obtain 

• Minimally invasive 

• Widely available 

• Relatively affordable 

Limitations

• Significant variability between products 

• Lack of standardization 

• Limited high-quality clinical evidence 

Best Suited For 

• Mild to moderate OA 

• Early intervention strategies 

• Performance horses requiring conservative management 

IRAP: Designed to Block Joint Inflammation 

IRAP focuses on increasing concentrations of interleukin-1 receptor antagonist (IL-1Ra), which counters one of the major inflammatory pathways involved in OA³. 

Potential Benefits 

• Targets inflammation more specifically 

• Useful for recurrent synovitis 

• May reduce reliance on repeated corticosteroid injections 

Current Evidence 

Several studies report clinical improvement, but high-quality blinded trials remain limited¹. 

Best Suited For 

• Horses with chronic inflammatory joint disease 

• Athletes requiring long-term joint management 

• Cases where corticosteroid use is less desirable 

Mesenchymal Stem Cells: The Regenerative Contender 

Stem cells have generated significant interest because of their ability to influence inflammation and potentially support tissue repair. 

In horses, MSCs may be harvested from: 

• Bone marrow 

• Adipose tissue 

• Umbilical cord tissue 

• Dental pulp 

• Muscle tissue⁴ 

What Makes MSCs Different? 

Unlike PRP or IRAP, MSCs possess immunomodulatory properties that may affect the joint environment beyond simple inflammation control. 

Current Evidence 

Among biologic therapies, MSC studies generally demonstrate stronger research design, including randomized and placebo-controlled trials. Overall clinical outcomes have been encouraging¹. 

Best Suited For 

• High-value sport horses 

• Chronic OA cases 

• Horses requiring long-term management plans 

The Standardization Problem 

One of the biggest challenges facing biologic therapies is inconsistency. 

Factors affecting the final product include: 

• Horse age 

• Health status 

• Collection technique 

• Processing methods 

• Cell concentration 

• Growth factor content 

As a result, two treatments labeled "PRP" or "MSC therapy" may differ significantly in biological composition and clinical effect⁵. 

Clinical Pearl 

Ask not only "Which biologic?" but also "How was it prepared?" 

What Does the Evidence Actually Say? 

A recent systematic review evaluating commonly used intra-articular therapies found: 

• PRP showed promising clinical improvement but lacked strong study design. 

• IRAP demonstrated beneficial effects, though evidence remains limited. 

• MSCs showed the most consistently positive outcomes among biologics. 

• Long-term safety and durability remain uncertain for all three therapies¹. 

Importantly, none of the reviewed studies reported serious adverse effects. 

Questions to Ask Before Recommending a Biologic 

Before selecting a biologic treatment, consider: 

1. What is the severity of OA? 

2. Is synovitis a major component? 

3. What are the owner's expectations? 

4. What is the horse's athletic goal? 

5. Is repeat treatment financially feasible? 

6. How strong is the evidence supporting the chosen product? 

These practical considerations often influence outcomes as much as the therapy itself.

The Future of Equine OA Treatment 

Biologics continue to represent one of the most exciting areas in equine medicine. However, practitioners should recognize that many products currently outpace the available evidence. 

Future advances will likely focus on: 

• Standardized preparation protocols 

• Better patient selection 

• Objective gait-analysis outcomes 

• Longer follow-up studies 

• Identification of true disease-modifying therapies 

Take-Home Message 

PRP, IRAP, and MSC therapies all offer potential benefits in equine OA management, but they should not be viewed as miracle treatments. Current evidence suggests MSCs have the strongest scientific support, while PRP and IRAP remain promising options in appropriately selected cases. For practising veterinarians, success depends on understanding both the strengths and limitations of each biologic and matching the therapy to the individual horse. 

References

1. Nedergaard A, Carlsson LE, Lindegaard C. Evidence of the clinical effect of commonly used intra‐articular treatments of equine osteoarthritis. Equine Veterinary Education. 2024 Dec;36(12):646-58. 

2. Brossi PM, Moreira JJ, Machado TS, Baccarin RY. Platelet-rich plasma in orthopedic therapy: a comparative systematic review of clinical and experimental data in equine and human musculoskeletal lesions. BMC veterinary research. 2015 Apr 22;11(1):98. https://link.springer.com/article/10.1186/s12917-015-0403-z 

3. Tokawa, P.K.A., Brossi, P.M. & Baccarin, R.Y.A. (2022) Autologous conditioned serum in equine and human orthopedic therapy: a systematic review. Research in Veterinary Science, 146, 34–52. https://pubmed.ncbi.nlm.nih.gov/35325755/

4. Gugjoo MB, Sharma GT. Equine mesenchymal stem cells: properties, sources, characterization, and potential therapeutic applications. Journal of equine veterinary science. 2019 Jan 1;72:16-27. https://doi.org/10.1016/j.jevs.2018.10.007

5. Mayet A, Zablotski Y, Roth SP, Brehm W, Troillet A. Systematic review and meta-analysis of positive long-term effects after intra-articular administration of orthobiologic therapeutics in horses with naturally occurring osteoarthritis. Frontiers in Veterinary Science. 2023 Feb 23;10:1125695. https://doi.org/10.3389/fvets.2023.1125695