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 bacteria