Polish researchers have examined how different kinds of injuries in thoroughbreds affect levels of the dominant biomarker for inflammatory response in horses.
Serum amyloid A (SAA) is the main acute phase protein in horses, massively released into the bloodstream in the initial phase of inflammation.
In horses affected by inflammatory disorders of the gut, respiratory and reproductive system, or developing complications after surgical procedures, SAA levels can exceed the normal range from 10 to 1000 times and may be useful in disease diagnosis, as well as forming a prognosis.
However, much less is known about the relationship between these acute phase proteins and disorders of the musculoskeletal system, Agnieszka Turło and her colleagues reported in the open-access journal, PLOS ONE.
Injuries to bone, muscle and tendon resulting from repetitive mechanical overload are the main health issues in performance horses. In racehorses, they are responsible for the greatest number of lost training days.
Early recognition of horses at risk of suffering injury is crucial, and blood biomarkers have been examined in that context.
Training-induced muscle, bone and joint trauma may result in an acute phase response reflected by changes in the blood concentration of SAA in racehorses.
However, it remained unclear if such a systemic reaction could be triggered by sport injuries and the impact of different types of musculoskeletal trauma on SAA concentrations in racehorses.
The study team, from the Warsaw University of Life Sciences–SGGW, set out to determine the changes in blood concentrations of SAA in racehorses with different types of musculoskeletal injuries.
The study involved 28 Polish thoroughbred racehorses diagnosed with injuries after racing. Seven had closed stress-related bone fractures, 11 had dorsal metacarpal disease, four had joint trauma, and six had tendon and muscle trauma. The researchers also used 28 healthy control racehorses in the study.
Serum samples were collected twice, between 1 and 4 days after the injury or, in the case of the control horses, after their successful completion of their race.
SAA concentrations in the samples were measured.
The researchers found that average SAA concentrations within the first four days of muscle and tendon injuries were significantly higher than in bone fractures, dorsal metacarpal disease, joint trauma or in the healthy horses. There were no significant differences between the other groups.
“Strain injuries of muscle and tendons can cause a moderate increase in SAA blood concentration in racehorses, reflecting the occurrence of the acute phase response,” the research team concluded.
A similar reaction was not observed in the stress-related bone injuries, they reported.
Discussing their findings, Turło and her colleagues said the results showed that tendonitis affecting the superficial digital flexor tendon and muscle injuries caused by exertion were the only injuries of the locomotor system among the study horses that resulted in SAA elevations when compared with the control group.
“Moreover, SAA levels in this group reached the values that are considered indicative for systemic reaction in horses with inflammatory diseases.”
They said the cases of bone injuries enrolled in their study showed different degrees of severity. However, all of the fractures were categorised as closed, stress-related lesions of the distal limb accompanied with limited soft tissue damage.
So, why do blood concentrations of SAA rise in the case of injuries to soft tissue structures, while damage to the bone and cartilage does not trigger such an increase?
“We cannot determine the cause of this difference,” they said, “although lower mass of the affected hard tissues and their reduced vasculature may be a limiting factor for the release of locally produced pro-inflammatory mediators … to the blood stream.”
They continued: “Injuries of muscle and tendon related to mechanical stress associated with race training can affect the serum level of SAA and should be considered in the interpretation of this biomarker in racehorses.”
Turło A, Cywińska A, Czopowicz M, Witkowski L, Niedźwiedź A, Słowikowska M, et al. (2015) The Effect of Different Types of Musculoskeletal Injuries on Blood Concentration of Serum Amyloid A in Thoroughbred Racehorses. PLoS ONE 10(10): e0140673. doi:10.1371/journal.pone.0140673
The full study can be read here.