Platelet-Rich Plasma (PRP) is a regenerative therapy used to treat horses with tendon and ligament injuries.

PRP is a blood preparation where plasma, the water and protein component of blood containing no cells, is mixed with highly concentrated platelets and injected into a site of injury. [1]

Administration of platelet-rich plasma delivers a concentrated dose of growth factors to the injury site on the horse’s body. The goal of treatment is to promote the repair process, improve healing, and speed tissue regeneration.

The use of PRP in horse is growing in popularity as injections can be tailored to the individual case. PRP injections are prepared using the horse’s own blood. The final composition of the injection can be adjusted during processing to target certain treatment outcomes.

Veterinarians primarily use PRP to treat tendon, ligament, and joint injuries. There is strong evidence supporting the use of PRP in tendons and ligaments, however more research is necessary to support other uses of this modality in horses.

Platelet-Rich Plasma Treatment in Horses

Platelet-rich plasma is a concentrated form of blood plasma that contains a high level of platelets and varying degrees of contaminating white blood cells. [1][16] Plasma also contains anti-inflammatory proteins, hormones, and antibodies that promote healing in damaged tissues. [1]

Platelets are cells primarily involved in blood clotting, however they also play a role in tissue repair and healing. [2] Platelets contain over 200 proteins including growth factors, which are proteins that stimulate cell proliferation to generate new tissue. [2]

When a platelet is activated, it releases stored proteins into the surrounding area. [2] In PRP treatment, the platelets are activated manually during preparation of the injection.

The release of growth factors by activated platelets is the basis for platelet-rich plasma treatment in horses. PRP increases levels of growth factor in a localized area to promote healing of damaged tissue. [2]

Preparation

To begin a platelet-rich plasma preparation, a small blood sample (approximately 60mL/2oz) is taken from the horse. [3] Specialized equipment is used to separate the plasma from the rest of the blood. [3]

Once the plasma is isolated, it is spun at high speed using a centrifuge to further concentrate it. [3] From 60mL of blood, the final volume of PRP product is typically around 10mL (0.3oz). [3]

Some veterinarians use a different preparation for PRP called V-PET, which does not require a centrifuge. [2] This system produces a platelet-only product that does not contain plasma. [2] Plasma-free preparations may have reduced antimicrobial function compared to traditional PRP preparations. [1]

Platelet Activation

Another aspect of PRP preparation is platelet activation. Activating platelets stimulates additional release of growth factors into the PRP preparation prior to injection. [1]

Methods of activation include: [2]

  • Freezing and thawing the PRP product
  • Addition of calcium chloride
  • Addition of bovine thrombin, the main protein that triggers platelet activation

Most veterinarians prefer calcium chloride activation. Adding bovine thrombin may increase the risk of inflammation in joints treated with activated PRP, and is now uncommon in veterinary practice. [1] Freezing and thawing can cause destruction of platelets and reduced growth factor release. [2]

There are also frozen forms of PRP available, called platelet lysates. These preparations typically have lower concentrations of growth factors and reduced antimicrobial effects compared to traditional PRP methods. [1]

Types of Platelet-Rich Plasma

After processing, the composition of platelet-rich plasma (PRP) is classified as either “pure” PRP or “leukocyte-rich” PRP based on the white blood cell content: [1]

  • “Pure” PRP contains primarily platelets with low numbers of white blood cells
  • “Leukocyte-rich” PRP has a high numbers of white blood cells

The type of PRP preparation produced depends on the technique used to isolate and concentrate the blood plasma. [1] This variation in final composition of the PRP product can alter its overall healing effects. [1]

Effects

Most studies on platelet-rich plasma focus on ligament, tendon, joint, and cartilage damage. There is extensive research into the effects of PRP on other tissues, particularly in human medical literature.

In cartilage and joints, reported effects of PRP include: [4][5]

  • Increased growth factors
  • Increased expression of genes associated with chondrocyte (cartilage cell) growth
  • Reduced pro-inflammatory mediators
  • Increased anti-inflammatory mediators
  • Improved healing of cartilage defects

In tendons and ligaments, reported effects include: [4]

  • Increased growth factors
  • Increased anti-inflammatory mediators
  • Increased production of collagen, the major structural protein of tendons and ligaments
  • Improved strength of healing tissues

One review showed 72.2% of PRP clinical trials in human and equine medicine had positive effects when treating joint disease. [6] 37% of studies on tendon disease and ligament disease had positive results. [6]

Antimicrobial Effects

There is some evidence that PRP may have an antimicrobial effect on tissues, meaning it could potentially help combat bacterial infections at the site of application. [1] Studies show that equine platelet proteins are effective against bacteria such as Staphylococcus, Streptococcus, and E. coli. [1]

One study in horses showed that joints treated with platelet proteins and antibiotics were less likely to show signs of infection and bacterial growth in joints infected with Streptococcus. [1] Horses receiving platelet proteins also had reduced damage to joint cartilage and decreased inflammation. [1]

These findings suggest PRP may have applications in treating septic arthritis (bacterial infection of a joint) in the future. [1]

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Clinical Use in Horses

One survey found 77% of equine practitioners use platelet-rich plasma as part of their clinical practice. [1]

Most veterinarians use PRP for joint, tendon, or ligament disease. PRP may also have applications in treating wounds, endometritis (uterine inflammation), and other injuries. [4][10][11]

Tendon and Ligament Injuries

To treat tendon and ligament disease, most veterinarians inject PRP directly into the damaged area. [1] In some cases, the area of injury is difficult to access for injection, so the veterinarian may inject the PRP into tissues surrounding the injury. [1]

There are several studies on the effect of PRP on tendon and ligament disease in horses. Clinical trials show PRP use has successfully supported tissue repair, with many horses returning to previous levels of performance.

One study treating several types of tendon and ligament injuries showed that 81% of horses returned to work within 6 months of treatment. [1]

Superficial Digital Flexor Tendon Injuries

In one study of injuries to the superficial digital flexor tendon, lameness decreased sooner after injury when PRP injections were used compared to untreated horses. [4]

80% of the treated horses returned to performance 12 months after treatment, whereas the untreated horses took 24 months to achieve a similar level of rehabilitation. [4]

Suspensory Ligament Injuries

A clinical follow-up study of nine Standardbreds with suspensory ligament injuries treated with PRP showed that all nine horses returned to racing. [7] The horses with suspensory ligament injuries had decreased earnings per race in the first year after treatment, but were otherwise performed similarly to their peers in competition. [7]

Another study on 100 Western performance horses showed that 75% of horses with proximal suspensory ligament injuries were sound at 1 year after receiving PRP treatment, with 67% actively in work. [8]

Finally, a study on English sport horses with long-term suspensory injuries showed that a platelet lysate product improved soundness at 6, 12 and 18 months after treatment. [9]

Sesamoiditis

Research shows horses with sesamoiditis are more likely to return to a racing career in the short-term when treated with PRP compared to horses that do not. [4] However, findings also show both treated and untreated horses have similar levels of performance in the long-term. [4]

Joint Disease

Veterinarians may inject platelet-rich plasma directly into a joint in cases of joint disease. [1] Goals of treatment include promoting tissue healing, increasing production of hyaluronic acid (a major lubricant within joints), and reducing inflammation. [1]

There are currently limited studies in equine medicine to support PRP as a joint treatment. [1] There are two studies in horses currently, which both concluded minimal efficacy of PRP.

The first study identified increased inflammatory mediators and decreased joint fluid quality 48 hours after PRP treatment of a joint. [4] From these results, the authors cautioned use of PRP in treating joints immediately after a surgical intervention, such as osteochondrosis dissecans treatment. [4]

Inflammatory reactions are considered to be more likely when using PRP containing high numbers of white blood cells.

The second study showed no beneficial effect of PRP injection into joints after surgery to repair meniscal tears in English sport horses. [1]

Other Uses

Platelet-rich plasma is also being explored as a treatment for other conditions in horses including bone healing, skin wounds, respiratory conditions, endometritis and laminitis.

Bone Healing

There is one case report of PRP use in a tibial fracture in a donkey. [4] The report identified increased healing at one month after PRP injection compared to the expected rate of recovery. [4] This finding is promising, but more research into the effect of PRP on bone fractures is needed.

Skin Wounds

There are conflicting results from studies on PRP use in treating skin wounds. [4]

One study showed PRP treatment reduced healing time on limb wounds by 15 days compared to controls. [10] Treated wounds were also less likely to develop severe granulation tissue (proud flesh).

In contrast, other studies show that PRP may promote excessive granulation tissue development. [11] One study of cannon bone wounds showed PRP treatment delayed wound healing for up to 3 weeks compared to untreated horses. [11]

These results suggest PRP may be most beneficial for old wounds that are no longer healing, or very large wounds. [11]

Endometritis

Use of PRP in uterine flushes shows promise as a treatment for post-breeding endometritis, a condition involving inflammation that occurs due to the uterine lining’s reaction to sperm.

Results from two studies showed mares treated with PRP have reduced uterine fluids and fewer inflammatory cells after artificial insemination compared to untreated mares. [4]

Another study showed that uterine PRP treatment shortened estrus cycle length and improved pregnancy rates in treated mares compared to the control group. [12] All mares in the study were “repeat breeders” who were unable to conceive in the previous three breeding cycles, so the researchers suggested that PRP may be a beneficial treatment for repeat breeder mares. [12]

Equine Asthma

There is one study reporting the use of PRP as a treatment for asthma in horses. In this study, the researchers administered PRP to the airways of horses with asthma. [13]

After treatment, horses with inflammatory airway disease, a mild form of equine asthma, showed less mucus in the airways and fewer inflammatory cells than before treatment. [13]

Laminitis

There is a study examining the effect of combined PRP and mesenchymal stem cell treatment for laminitis in horses. [14]

In the study, nine horses treated for laminitis returned to their previous activity within six months of laminitis developing, with seven of them still active one year after treatment. [14] Two horses developed another episode of laminitis before the 1-year mark. [14]

Since both PRP and mesenchymal stem cells were part of the treatment, the effect of PRP on its own in treating laminitis is unknown. [14]

Burns

One study examined the effect of PRP treatment on healing of deep second-degree burns in horses. [15] Horses that received PRP treatment showed increased healing compared to control horses, but also showed increased scar tissue formation. [15]

Side Effects

Reports of adverse effects from PRP injection in horses are rare. Since the horse’s own blood is used to prepare PRP treatments, there is minimal risk of an immune reaction to the PRP injection. [1][6]

According to a survey of equine practitioners, less than 2% of horses develop joint flares (an immune reaction to a joint injection) after PRP injection. [1]

PRP injections must be administered carefully and should only be performed by a qualified practitioner to reduce the risk of adverse reactions. Undesired leakage of PRP fluid into tissue other than the intended injection site may cause scarring and unwanted tissue proliferation. [1]

To prevent this from occurring, veterinarians typically measure the size of the damaged area using ultrasound to calculate an appropriate volume of PRP.

Possible side effects from PRP injection include: [1][2]

  • Local inflammation and pain at the injection site
  • Infections at the injection site
  • Widespread inflammation throughout the body

Techniques to reduce local inflammation including icing the area after PRP application and administration of non-steroidal anti-inflammatory drugs (NSAIDs). [2]

Use of NSAIDs after PRP injection is somewhat controversial, as some practitioners believe NSAIDs reduce the release of growth factors from platelets based on studies from human medical literature. [2] However, horse platelets show little response to common equine NSAIDs, such as phenylbutazone, and are considered safe to use in combination with PRP treatment. [2]

Supporting your Horses’s Joints, Tendons, and Ligaments

If your horse has ongoing joint health issues or is recovering from an injury, consider discussing options with your veterinarian and equine nutritionist.

Providing a balanced, forage-based diet that meets all vitamin and mineral requirements should be the foundation for any horse. Y

You can also support the horse’s own homeostatic counterregulatory responses to inflammation by feeding additional supplements such as MSM and w-3 oil (which contains the anti-inflammatory omega-3 fatty acid DHA).

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  • Supports joint health
  • Cartilage & connective tissue
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Summary

Platelet-rich plasma (PRP) treatment for horses is growing in popularity as its multiple clinical uses continue to show promise in scientific study. In horses, it is most commonly used to promote healing and rehabilitation in tendon and ligament injuries.

  • Platelet-rich plasma involves injecting plasma into an area of injury to promote healing
  • PRP is common for treating tendon, ligament, and joint injuries in horses
  • There is good evidence to support the use of PRP in tendon and ligament injuries, but more research is required for other uses
  • PRP is safe with few reported side effects when administered by a trained professional

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References

  1. McCarrel, T. M. Equine Platelet-Rich Plasma. Veterinary Clinics of North America: Equine Practice. 2023.
  2. Textor, J. Autologous Biologic Treatment for Equine Musculoskeletal Injuries: Platelet-Rich Plasma and IL-1 Receptor Antagonist Protein. Veterinary Clinics of North America: Equine Practice. 2011.
  3. Restigen® PRP – Platelet Concentration Kit Instructions. Zoetis Equine.
  4. Camargo Garbin, L. et al. A Critical Overview of the Use of Platelet-Rich Plasma in Equine Medicine Over the Last Decade. Front. Vet. Sci. 2021.
  5. Pérez Fraile, A. et al. Regenerative Medicine Applied to Musculoskeletal Diseases in Equines: A Systematic Review. Veterinary Sciences. 2023.
  6. Brossi, P. M. et al. 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.
  7. Waselau, M. et al. Intralesional Injection of Platelet-Rich Plasma Followed by Controlled Exercise for Treatment of Midbody Suspensory Ligament Desmitis in Standardbred Racehorses. J Am Vet Med Assoc. 2008.
  8. Giunta, K. et al. Prospective Randomized Comparison of Platelet Rich Plasma to Extracorporeal Shockwave Therapy for Treatment of Proximal Suspensory Pain in Western Performance Horses. Research in Veterinary Science. 2019.
  9. Maleas, G. and Mageed, M. Effectiveness of Platelet-Rich Plasma and Bone Marrow Aspirate Concentrate as Treatments for Chronic Hindlimb Proximal Suspensory Desmopathy. Front Vet Sci. 2021.
  10. Pereira, R. C. D. F. et al. Evaluation of Three Methods of Platelet-Rich Plasma for Treatment of Equine Distal Limb Skin Wounds. Journal of Equine Veterinary Science. 2019.
  11. Monteiro, S. O. et al. Effects of Platelet-Rich Plasma on the Repair of Wounds on the Distal Aspect of the Forelimb in Horses. American Journal of Veterinary Research. 2009.
  12. Dawod, A. et al. Effect of Intrauterine Infusion of Equine Fresh Platelets-Rich Plasma (PRP) or Lyophilized PRP (L-GFequina) on Ovarian Activity and Pregnancy Rate in Repeat Breeder Purebred Arabian Mares. Animals. 2021.
  13. Dzyekanski, B. et al. Intrabronchial Instillation of Platelet-Rich Plasma in Equines with Inflammatory Airway Disease – Preliminary Report. Estud Biol. 2012.
  14. Angelone, M. et al. The Contribution of Adipose Tissue-Derived Mesenchymal Stem Cells and Platelet-Rich Plasma to the Treatment of Chronic Equine Laminitis: A Proof of Concept. International Journal of Molecular Sciences. 2017.
  15. Maciel, F. B. et al. Scanning Electron Microscopy and Microbiological Evaluation of Equine Burn Wound Repair after Platelet-Rich Plasma Gel Treatment. Burns. 2012.
  16. Radtke, A.V. et al. Platelet and Leukocyte Concentration in Equine Autologous Conditioned Plasma Are Inversely Distributed by Layer and Are Not Affected by Centrifugation Rate. Front Vet Sci. 2020.