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Draft horses competing in the Calgary Stampede’s Heavy Horse Pull are so strong they can pull a load five times their body weight — as much as 5,000 kilograms. The workload demands of this intensive competition are drastically different from other disciplines and little is known about how it affects the health of these giant equines.

Researchers at the ��ݮ����Ƶ����  (UCVM) want to better understand the physiological effects of the competition.

“The pulling competitions are very interesting to me because they’re a unique type of horse doing a unique type of exercise,” says  associate professor of equine internal medicine at UCVM and Calgary Chair of Equine Sports Medicine. “It’s a very short-duration, high-burst-of-energy expenditure and not much is known about how the competition affects them physiologically.”

Historically, draft horses have been selected to pull slowly over long distances tirelessly, but Persephone Greco-Otto, a graduate student working on the project, says the heavy pull exercise is pure force and power for only a few seconds, so the competition is a very different demand from what the horses were bred to do.

“Heavy horses have essentially been ignored in research, with the only work focusing on the long-duration, low-weight pulling associated with farming,” says Greco-Otto. “The demands of the Heavy Horse Pull are very different, but have never been explored.”

Weight loss, dehydration and electrolyte imbalances

In the  teams of two draft horses pull a weighted sled over 14 feet at an increasing load until a maximum is reached. Besides the demands of the actual competition, the horses may be exposed to a number of pre-competition stressors including being trailered long distances. This can result in weight loss, dehydration, and electrolyte imbalances.

“With this study we’re looking at the effect on their metabolism, so electrolytes, body water content, kidney function and muscle response to not only their shipping but also to the pulling competition,” says Leguillette. “Specifically, by monitoring weight, blood chemistry, electrolytes, and high-sensitivity cardiac troponin (hscTnT) — a highly specific cardiac biomarker. We’re also investigating the effect of rapid weight change on performance. ”

The teams of horses are weighed when they arrive at the Stampede and are assigned to compete in one of three classes: light, middle and heavyweight. Similar to some human athletes such as wrestlers, some horses also undergo rapid weight loss beforehand in order to gain a competitive edge by qualifying for entry in a lower weight category, before recovering the lost weight at the time of the competition, one to three days after the weigh-in. The physiological effects of this practice are currently unknown in horses.

Leguillette and his research team weigh horses taking part in the study on arrival and again on the day they compete. They measure each horse’s body length and circumference, and gather data on their age, hauling distance, last feeding, and last water prior to arrival. 

High-tech research in the barn

They also take blood samples and use a bio-impedance device to measure each horse’s water and fat content.

“The bio-impedance device is a non-invasive way to look at the body contents, fat and fluid,” explains Leguillette as he places acupuncture-like needles in the neck and rump of a Belgian draft horse. “You connect the neck to the hind end, so basically the whole length of the horse and you’re measuring how well the body will conduct electricity with a very low-volt current. It’s a very precise technique that’s used in humans but hasn’t been used in draft horses before.”

The goal of all these measures is to gain a good picture of body water and fat content when the horses arrive and then compare the same picture one to three days later when they compete.

The study, now in its second year, is yielding results. It’s found a substantial change in body weight from arrival to competition, indicating the horses are hydrated and have recovered from shipping by the time they enter the arena to compete.

 “We’ve found that their blood is very concentrated when they arrive on site but then they get rehydrated. We give recommendations to the owners and trainers on electrolytes supplementation,” says Leguillette. 

“The key is really that, contrary to many human athletes like wrestlers, these horses are fully hydrated when they are competing, which is good news.”