Sudden collapse behind most band deaths in Norway and Sweden’s trotting study
Most deaths on racetracks in racehorses in Sweden and Norway are the result of a sudden collapse rather than catastrophic injuries, recent research shows.
Ingunn Risnes Hellings and her research colleagues set out to explore racing-related deaths in Norwegian and Swedish racehorses, by crossing incidence rates, risk factors and important findings after slaughter.
They looked at deaths over a six-year period from 1 January 2014 to 31 December 2019, using the registers of the Norwegian and Swedish trotting associations.
In an attempt to identify risk factors, the study team looked at race, age, gender, frequency of competition starts, competition distance at the time of death and time of year.
Whether the horse competed in a trotting race under a saddle or a regular harness race was also registered.
Deaths were included if they involved a seemingly healthy horse that died suddenly or was killed after injury immediately before the start, during or within an hour after the race.
A total of 48 horses died during the study period, which included 38 standard breeds and 10 Norwegian-Swedish cold-blooded trotters.
Thirty-three of the deaths occurred in Sweden and 15 in Norway.
The total number of competition starts during the study period was 816,085, of which 576,162 in Sweden and 239,923 in Norway.
This meant that there were 0.059 deaths per 1,000 competition starts for the two countries together. The total figure for Sweden was 0.057 while in Norway it was 0.063 per 1000 starts.
The researchers found that the proportion of deaths attributed to catastrophic orthopedic / traumatic injuries was 14.5%, while the rest was attributed to what they called sudden athletic death.
The high number of sudden deaths that cannot be attributed to a serious track injury differs markedly from previous reports of thoroughbred competition horses, where most competition-related deaths are due to catastrophic orthopedic injuries. In whole blood, sudden athletic mortality varies from 9% to 19%.
The authors found that higher numbers of starts in the last 30 days increased the risk of sudden death in trotters. “It is conceivable, although speculative at this time, that frequent competition starts within a short period of time could increase myocardial damage with little time for tissue repair,” they said.
An opposite effect was observed with the number of starts in the last 180 days. “Provided that the horses have had time to recover sufficiently between races, which means that any heart damage can heal, this may reflect that the horses were better conditioned. However, this remains a speculation.”
The number of horses included in the study was too few to draw any definite conclusions about the risk of sudden athletic death and its association with the frequency of race starts, they said.
Seven of the 48 horses were killed due to catastrophic injuries.
Acute circulatory collapse due to suspected heart or lung failure, or both, was recorded in 30 horses, while major bleeding after vascular rupture was the primary cause of death in 10 cases. A horse collapsed and died but was not submitted for autopsy.
Postmortem findings included pulmonary edema, blood clotting and bleeding, major vascular rupture, and macro- and microscopic heart changes.
While 70 percent of the 40 horses in the category of sudden athletic death 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 investigating pathologist.
The authors noted that the total proportion of racing-associated death and sudden athletic death was remarkably similar between the two races in the study.
The researchers described the incidence of catastrophic orthopedic deaths in the study as comparatively low, while confirmed or suspected cardiopulmonary causes and the incidence of sudden death were similar to previous studies.
“Determining the underlying pathophysiological causes of these latter cases remains a major challenge, requiring further investigation,” they said.
The study team consisted of Hellings, Eystein Skjerve, Carl Fredrik Ihler and Constanze Fintl, all with the Norwegian University of Life Sciences; Erika Karlstam, with the Swedish Veterinary Institute; and Mette Valheim, with the Norwegian Veterinary Institute.
Competition-related deaths in Norwegian and Swedish racehorses: Incidence rate, risk factors and main findings after slaughter
Ingunn Risnes Hellings, Eystein Skjerve, Erika Karlstam, Mette Valheim, Carl Fredrik Ihler, Constanze Fintl
Journal of Veterinary Internal Medicine, January 21, 2022, https://doi.org/10.1111/jvim.16364
The study, published under a Creative Commons license, can be read here.