Uneven movement at the trot was detected in most of the 103 Standardbred yearlings used in a Scandinavian study.
The movement asymmetry detected in the study, reported in the Equine Veterinary Journal, was measured objectively using wireless inertial sensors fitted to the horses.
The researchers from the Norwegian University of Life Sciences and the Swedish University of Agricultural Sciences recruited the support of 12 trainers in Norway and Sweden for the study.
All the horses, with an average age of about 18 months, had been started in harness and were in the early months of training for racing. All were considered fit to train by their trainers.
The yearlings were studied at the start of their careers to reduce the chances of training‐related injuries being present.
Anne Kallerud and her colleagues noted few studies to date have provided objective measurement of movement in Standardbreds. This meant little was known about biological variation and clinical significance of measured movement asymmetry in the breed.
All horses in the study underwent a physical examination beforehand, and details were taken of the sex, height, track type, in-hand measurements and the individual trainers to see whether any associations could be found with any uneven movement that may be detected.
Of the 103 horses, 77 were evaluated both in‐hand (the handler trotting them out while giving them free head carriage) and on the track; a total of 24 were assessed in‐hand only, and two were assessed only on the track. For all track trials, the horses had their usual driver and wore their regular tack.
Using thresholds established for other breeds, the study team found that 94 of the horses — that’s 93% — showed front and/or hindlimb asymmetry in the in-hand trials. In the track trials, 74 horses, or 94%, showed asymmetry.
Most asymmetry seen was mild, they said, and one in five horses switched the side of their asymmetry for one or more parameters between their in‐hand and track trials.
Discussing their findings, the researchers say it is unknown whether movement asymmetry increases, decreases or stabilises with age and training.
Movement asymmetry was prevalent in the group, with considerable individual variation between trials. Within‐trial variability was also high, influencing the reliability of the data.
It was unclear whether the study team had measured widespread and previously undetected subclinical, pain‐mediated disease or whether the asymmetry seen was biological variation, which might vary across breeds and disciplines.
The study had explored the prevalence of asymmetry, not its underlying causes.
“One might argue,” they said, “that it is improbable that almost all yearlings in a cohort could be affected by orthopaedic pain, especially at such an early age and prior to any substantial training.”
As in young children, stabilisation of movement frequency and pattern might increase with maturity and better neuromuscular control, they said.
Future studies should look at changes in asymmetry over time and explore any associations between measured movement asymmetry and the development of clinical lameness.
The study team comprised Kallerud and Cathrine Fjordbakk, with the Norwegian University of Life Sciences; Eli Hendrickson, with the Norwegian Veterinary Association; and Emma Persson‐Sjodin, Marie Hammarberg, Marie Rhodin and Elin Hernlund, all with the Swedish University of Agricultural Sciences.
Objectively measured movement asymmetry in yearling Standardbred trotters
Anne S. Kallerud, Cathrine T. Fjordbakk, Eli H. S. Hendrickson, Emma Persson‐Sjodin, Marie Hammarberg, Marie Rhodin and Elin Hernlund
Equine Veterinary Journal, 19 June, 2020, https://doi.org/10.1111/evj.13302