Platelet-rich plasma (PRP) is a form of regenerative therapy used to treat soft-tissue injuries in athletes. Platelets in blood contain growth factors that stimulate cells in injured tissue to begin healing and to draw new cells to the injured area.
Over the past two decades, veterinarians have achieved much success with PRP in treating tendon, ligament, and muscle injuries and in wound healing. In 2016, California stakes winner Bettys Bambino came back after PRP treatment for a ligament injury to win the Grade 3 San Simeon Stakes at Santa Anita Park by 2-1/4 lengths.
PRP is derived from the patient's own body, so it does not cause rejection complications. Blood is drawn from the patient and centrifuged to separate the white and red blood cells for removal and to concentrate the platelets in the plasma. The PRP is then injected at the site of the injury.
Human reproductive specialists began using PRP in 2004 to treat endometritis, an inflammation of the lining of the uterus that causes infertility. Seeing their success, researchers in equine reproductive medicine began to explore the possibility that PRP might be useful in mares that experience persistent breeding-induced endometritis. One of those researchers is Dr. Lisa Metcalf, assistant professor at Oregon Health & Science University in Portland who specializes in theriogenology (reproduction).
Metcalf explained that all female mammals develop inflammation and fluid in the uterus after breeding as a means for the body to rid the uterus of harmful bacteria and other bi-products of inflammation that result from the sperm at breeding.
“The fertilized ovum becomes an embryo that travels in the fallopian tube or oviduct for five days before dropping into the mare's uterus,” she said. “The normal mare clears that inflammation and fluid very rapidly. Clearance of the inflammation follows quickly, too. So by that five days, the uterus is quiet, with no inflammatory cells and no fluid in that environment detrimental for the embryo.”
Mares that are unable to clear the inflammation and fluid deliver the embryo into a hostile environment in the uterus that ultimately results in destruction of the embryo. The problem created is not inability to conceive, but inability to maintain the pregnancy.
Most of the work with PRP in mares with persistent breeding-induced endometritis has been done using artificial insemination, but Metcalf said it also can be utilized in mares bred by live cover.
“Persistent breeding-induced endometritis occurs in mares whether it is artificial insemination or natural cover,” she said. “It's actually the sperm that causes this inflammatory reaction, so it doesn't matter how the sperm gets there.”
After the blood is drawn from the mare and centrifuged to produce PRP, it is infused into the uterus via an intrauterine catheter inserted through the cervix. In the uterus, PRP modulates inflammation and increases blood flow to tissues. This rids the uterus of unwanted fluid to prepare it to accept and nurture the embryo.
“Basically, the procedure is to take 180 milliliters of blood that is mixed with an anticoagulant, and we perform a double spin in a centrifuge to isolate the platelets,” she said. “ Out of that 180 milliliters you only end up with between 2-5 milliliters of concentrated platelets, or platelet-rich plasma. … Any veterinarian who performs reproduction services can do it. Often they already have PRP machines in their clinic because they're using it for tendons, joints, and wound healing.”
Metcalf cautioned the PRP produced should be “lesion-specific” for this purpose. For instance, PRP used for joint and soft-tissue injuries will not contain the white blood cells found in PRP that is ideal for treating endometritis.
Metcalf infuses PRP into the uterus 24 to 36 hours before breeding, but other researchers perform the infusion after the mare is bred. No study has definitively found which timing is better — before or after. Metcalf said much more work is needed in this area.
“Anecdotally, I can actually palpate a difference in uterine tone following PRP because these susceptible mares often present with a big, sloppy uterus; and what I feel in there the day after I infuse PRP is a remarkable increase in tone. Suddenly, the uterus snaps into shape,” Metcalf said.
Metcalf first published her study results in 2013, but she has used PRP treatment for persistent-breeding-induced endometritis for the past decade.
“I'm glad there's interest in this. It's one of my silver bullets for mares susceptible to persistent breeding-induced endometritis,” she said.
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