Sudden collapse behind most track fatalities in Norway and Sweden’s trotters – study

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Most racetrack fatalities in harness racehorses in Sweden and Norway are a result of sudden collapse rather than catastrophic injuries, fresh research shows.
A Coldblooded Trotter of mixed Swedish and Norwegian lines. Photo: Don Wright, CC BY 2.0 via Wikimedia Commons

Most racetrack fatalities in harness racehorses in Sweden and Norway are a result of sudden collapse rather than catastrophic injuries, fresh research shows.

Ingunn Risnes Hellings and her fellow researchers set out to explore racing-associated fatalities in Norwegian and Swedish harness racehorses, traversing incidence rates, risk factors, and key postmortem findings.

They looked at fatalities over a six-year period from January 1, 2014, to December 31, 2019, using the records of the Norwegian and Swedish Trotting Associations.

In a bid to identify risk factors, the study team looked at breed, age, sex, the frequency of race starts, the racing distance at the time of death, and the time of year.

Whether the horse competed in a trotting race under saddle or a regular harness race was also recorded.

Fatalities were included if they involved an apparently healthy horse that died suddenly or was euthanized after injury immediately before the start, during, or within an hour of racing.

A total of 48 horses died during the study period, which included 38 Standardbreds and 10 Norwegian-Swedish Coldblooded Trotters.

Thirty-three of the deaths occurred in Sweden and 15 in Norway.

The total number of race-starts during the study period was 816,085, of which 576,162 were in Sweden and 239,923 in Norway.

This meant there were 0.059 deaths per 1000 race-starts for the two countries combined. The overall figure for Sweden was 0.057 while in Norway it was 0.063 per 1000 starts.

The researchers found that the proportion of fatalities attributed to catastrophic orthopedic/traumatic injuries was 14.5%, while the rest were attributed to what they termed sudden athletic death.

The high number of sudden deaths not attributable to a serious track injury differs markedly from previous reports in Thoroughbred racehorses, where most racing-associated deaths are due to catastrophic orthopedic injuries. In Thoroughbreds, sudden athletic death rates vary from from 9% to 19%.

The authors found that higher numbers of starts within the last 30 days increased the risk of sudden death in trotters. “It is conceivable, although at this point speculative, that frequent race-starts within a short period could increase myocardial damage with little time for tissue repair,” they said.

An opposite effect was observed with the number of starts over the last 180 days. “Assuming that the horses have had time to recover sufficiently between races, allowing possible myocardial injuries to heal, this could reflect that horses were better conditioned. However, this remains a speculation.”

The number of horses included in the study was too few to draw any firm conclusions on the risk of sudden athletic death and its association with frequency of race starts, they said.

Seven of the 48 horses were euthanized because of catastrophic injury.

Acute circulatory collapse because of suspected cardiac or pulmonary failure, or both, was recorded in 30 horses, while major hemorrhage after vessel rupture was the primary cause of death in 10 cases. One horse collapsed and died but was not submitted for autopsy.

Postmortem findings included pulmonary edema, congestion and hemorrhage, major vessel rupture, as well as macro-and microscopic cardiac changes.

While 70 percent of the 40 horses in the sudden athletic death category had marked bleeding in the lungs, only three of these 28 horses had exercise-induced pulmonary hemorrhage listed as the definitive cause of death by the examining pathologist.

The authors noted that overall rates of racing-associated death and sudden athletic death were remarkably similar between both breeds in the study.

The researchers described the rates of catastrophic orthopedic fatalities in the study as comparatively low, while confirmed or suspected cardiopulmonary causes and incidence rates for sudden death were similar to previous studies.

“Determining the underlying pathophysiological causes of these latter cases is still a major challenge, which needs further investigation,” they said.

The study team comprised Hellings, Eystein Skjerve,Carl Fredrik Ihler and Constanze Fintl, all with the Norwegian University of Life Sciences; Erika Karlstam, with the Swedish National Veterinary Institute; and Mette Valheim, with the Norwegian Veterinary Institute.

Racing-associated fatalities in Norwegian and Swedish harness racehorses: Incidence rates, risk factors, and principal postmortem findings
Ingunn Risnes Hellings, Eystein Skjerve, Erika Karlstam, Mette Valheim, Carl Fredrik Ihler, Constanze Fintl
Journal of Veterinary Internal Medicine, 21 January, 2022, https://doi.org/10.1111/jvim.16364

The study, published under a Creative Commons License, can be read here

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