Stress on endurance horses probed in study

Endurance horses generally cope well with the stresses of racing, a study suggests.

The conclusion was based on the assessments, including electrocardiograms and blood chemistry analysis, of horses who competed in two endurance events – one in Norway and one in Denmark.

“This study would indicate that, based on the analyzed parameters, endurance horses cope well with the stress and physical demands of endurance racing,” the Scandinavian researchers concluded.

“Many of the changes in blood biochemistry seem to be grounded in a decreased blood volume, an increased energy expenditure, and exercise-related muscular damage.”

The decreased blood volume was primarily the result of sweat loss and a low fluid intake, the scientists found.

“Significant changes in muscle parameters were found in both races, and in race A these were found to be correlated negatively with competition experience.”

The researchers, whose findings have been published in the journal, ISRN Veterinary Science, noted the rise of popularity of endurance as a sport.

“This interest in the sport makes it ever more important to ensure that any adverse effects on the horses as a result of such a physically demanding race are minimized.”

There was a need for techniques to accurately assess the health and well-being of competing horses, noted the researchers, most of whom are based at Copenhagen University.

“To this end, the current findings indicate that the heart score method does not seem to be of great use when assessing the performance potential of an individual endurance horse.

“Rather, it seems that to improve performance there is a need for further studies on how rehydration of endurance horses is to be best managed.”

The first race in the study was the Nordic and Baltic Endurance Ride Championships in Magnor, Norway, in 2005, in which 15 horses racing on a 120km course were studied by agreement with their owners.

The second race was in May 2007 at the Racing Ground, in Dronninglund, Denmark, involving 16 horses racing between 65km and 120km.

The researchers said their analysis focused on blood paramaters, heart scores and and fluid use. All horses underwent an electrocardiogram before competing for use in correlating back against their heart scores after competition. In all cases, blood samples were taken before and after racing.

They said they noted no correlation between heart score and speed, but a significant correlation was found between fluid intake and average speed.

They said evaporative heat loss in endurance horses can be 10–15 liters per hour, primarily as sweat. Net fluid deficits of 20 to 40 liters after rides of more than 80 kilometers are common.

Weight losses of 4–7% of body weight in connection with endurance racing have been found in several studies, primarily due to uncorrected sweat loss. Performance is affected with even a 3% level of dehydration, they said.

“What is clear is that electrolyte loss during an endurance race is greatly influenced by temperature, humidity, type of terrain, and the length of a ride.

“Moreover, evidence suggests that electrolyte disturbances are most severe 30 minutes after finishing a 100km race compared to before, mid, or immediately after a race.

“However, data as to how horses should be rehydrated to avoid illness and death after an endurance race are far from clear, especially since no one race can easily be compared with another due to differences in climate and terrain.

“Of particular noteworthiness in this connection is the case of a horse that died after a race in South Africa, due to severe dehydration followed by free access to water (e.g., osmotic shock).”

Training, they said, has been shown to increase a horse’s capacity for heat expenditure, raising heat tolerance, and lowering the core temperature for aerobic exercise, making this an important aspect to be included in the preparations needed for a successful race.

“Cooling was found to correlate positively and significantly with higher speeds.

“A significant correlation was also found between the total number of kilometers experienced in competition racing and the amount of water used for cooling.

“This could indicate that the human tendency for earlier and greater sweat production in well-trained individuals, proposed by McKeever and colleagues, could in fact also apply to horses.

“Indeed, in support of this, we have found that there was a strong tendency for larger amounts of cooling water used early in the race to improve the final distance covered under competitive racing.

“The cooling water used was on average 29.75 liters, whilst for the 120km class it was 57.75 liters.

“These horses worked for 8.5–10.0 hours, which would result in a calculated fluid loss of approximately 85–150 liters.

“Since one might anticipate that the amount of water needed for cooling is related to the degree to which a horse sweats, future studies should perhaps now focus on how much water cooling can influence the need to sweat.”

J. Larsson, P. H. Pilborg, M. Johansen, et al., “Physiological Parameters of Endurance Horses Pre- Compared to Post-Race, Correlated with Performance: A Two Race Study from Scandinavia,” ISRN Veterinary Science, vol. 2013, Article ID 684353, 12 pages, 2013. doi:10.1155/2013/684353

The full study can be read here.