Autologous conditioned serum is a cell-free extract of whole blood that has been processed to contain high concentrations of naturally occurring anti-inflammatory proteins. Josephine Hale, BVetBio/BVSc, MANZCVS, of Charles Sturt University, in Wagga Wagga, New South Wales, says a single bout of intense exercise reduces important anti-inflammatory cytokine (cell-signaling protein) concentrations in whole blood while increasing pro-inflammatory cytokine levels. Essentially, this means the ACS produced from post-exercise blood is less anti-inflammatory.

“The timing of when to collect ACS is often related to when it suits the owner for the horse to be available, and not so much around the exercise schedule,” she said. “Hopefully, this can be useful information for people to consider in their timing.”

Researchers in both human and equine medicine have already shown that intense exercise triggers an acute inflammatory response in the body, which is associated with greater concentrations of pro-inflammatory cytokines. That might be due to the (usually short-term) traumatic effects of training on bones, muscles, and joints, she said. In 2015, Norwegian researchers found that the stress from castration surgery could affect ACS quality.

Suspecting exercise would change the anti-inflammatory character of ACS in horses, Hale and her fellow researchers analyzed whole blood from eight healthy, sound Standardbreds, ages 2 to 8 years old, in active harness race training. The researchers drew blood just before the four mares and four geldings underwent a training session, trotting for one mile at peak speeds on a sand track, then an hour later, and again 23 hours after that.

The team processed ACS from each of the whole blood samples after the standard 24-hour incubation time. They then investigated the serum using fluorescent microsphere immunoassay.

Exercise affected neither the anti-inflammatory cytokine interleukin-10 (IL-10) nor the pro-inflammatory Interleukin 1β (IL-1β), she said.

However, at one hour post-exercise, concentrations of the anti-inflammatory mediator interleukin 1 receptor antagonist (IL-1Ra) were significantly reduced. And at the same time, tumor necrosis factor α (TNF-α) concentrations had significantly increased.

Given what scientists already know about changes in cytokine concentrations related to stress and exercise, the results weren’t particularly surprising, said Hale.

“It wasn’t a big leap to expect that that was going to happen in a potentiated blood product like ACS,” she said.

Still, it’s not something she or most people have traditionally considered as a possible side effect of exercise, she added.

Those effects were visible even in healthy and fit racehorses in regular training programs, she added. The changes in cytokine concentrations in ACS were significant even though the horses showed no signs of systemic inflammation, according to whole blood analyses, after their workouts. All their other blood parameters—serum amyloid A (SAA), protein, albumin, and globulin, as well as cortisol—were also within normal range. As expected, however, the horses’ lactate concentrations were at least three times higher than before exercise.

Typically there’s a balance of anti-inflammatory and pro-inflammatory cytokines in healthy joints, said Hale. In osteoarthritic joints, however, that balance is upset as TNF-α and IL-1β expression increases without corresponding increases in IL-1Ra. One of the main benefits of ACS, she explained, is that it should provide higher concentrations of anti-inflammatory cytokines IL-1Ra and IL-10, as well as several growth factors.

The new study reveals this might not be the case with ACS produced from blood drawn just after exercise, said Hale. That’s particularly important information for owners who choose to have their veterinarian administer ACS injections in their sport horses with mild or well-managed osteoarthritic lesions. “Even though the horse might be quite sound at the moment, continuing to apply that therapy might help them as the big competition approaches,” she explained.

Further studies might investigate additional time points to more accurately determine when the concentrations return to their pre-exercise levels, she added.

“Even though we looked at this in racehorses, we think performance horses too,” Hale said.