They’re in their own unique sector of active equids—and their welfare has been significantly understudied, said Sina Huwiler, BSc, who’s working under the supervision of professor Conny Herholz, PD, DrMedVet, FTA, Dipl. ECEIM, ATA, at the Bern University of Applied Sciences School of Agricultural, Forest, and Food Sciences (HAFL), in Switzerland.
“Pack mules fall into a sort of scientific desert, often overlooked by researchers,” Huwiler said. “But these animals are used year after year, rented out by their owners to tourists who often have no experience with equids at all. It’s important to explore what’s going on with these pack mules during their trips and how well they fare during the voyage.”
Huwiler and her fellow researcher, Marie Pfammatter, BSc, also a student at HAFL, followed a film crew producing a documentary as they crossed the St. Gotthard Pass (a mountain pass in the Alps that connects northern and southern Switzerland). The crew rented three mules to carry their equipment over a five-day journey. The scientists took regular measurements of the mules’ heart rates, respiratory rates, body temperatures, and fecal cortisol levels to monitor their stress levels. Huwiler presented their findings at the 2018 Swiss Equine Research Day.
The mules—two females and one male aged 12, 19, and 24 years old—dealt with the physical and emotional stress very well, the researchers said. They carried packs weighing about 80 kilograms (175 pounds) each to altitudes of more than 2,000 meters (6,500 feet). Despite these challenges, the mules had good recovery heart rates ranging between 40 and 72 beats per minute, Huwiler said.
“As a comparison, during endurance races of 80 to 160 kilometers (50 to 100 miles), horses are allowed to continue to race at the vet checks if heart rates drops under 64 beats per minute,” she explained. “One of the mules was ridden once, and during that time it was possible to measure the heart rate continuously with a heart rate meter. The heart rate never raised above 150 beats per minute, which corresponds to a performance level at an endurance (aerobic) level.”
The mules’ cortisol levels rose somewhat on the second day, then plateaued for the rest of the journey up until the fifth day, when all three reached levels indicating significant stress, said Huwiler. “It was clear that if the excursion had continued a sixth day, they would have needed a rest day to recover before continuing,” she said.
Overall, Huwiler said, the animals dealt with the long and sometimes difficult journey well—far better than the scientists had expected they would, she added.
“These are surprisingly hardy animals, coping with the physical and emotional stresses of such an adventure quite well,” she said.
Even so, these findings shouldn’t lead people to take advantage of mules’ hardiness, she added. “They’re tough, but they do have their limits,” she said. “That fifth day of work was really a maximum for them in those conditions.”