Using Body Language to Assess Fatigue in Working Horses
After a long day working the ranch, you’d expect a horse to be tired. But tiring to the point of exhaustion is bad for his welfare, researchers say. How can you tell whether a working horse is simply tired or full-out fatigued? The answer, according to a new study, might be written all over his body.

Horses communicate their physical state of tiredness and even soreness after work through their facial expressions and weight-shifting patterns, said Pedro Henrique Esteves Trindade, PhD candidate at São Paulo State University, in Jaboticabal, Brazil.

Many owners and riders already intuitively recognize the body language of tired horses, Trindade said. But by applying science to these observations, researchers can develop an ethogram (behavior chart) that handlers can use to concretely identify signs that their horses’ welfare is at risk due to overwork.

“Scientists can take these body language indicators and establish classifications of intensity of physical tiredness (using dose-response studies),” he explained. “After these steps, the most powerful indicators can be used on farms to recognize physical tiredness before the animal reaches deleterious levels of fatigue or physical exhaustion. This will be important to determine the workload and also the rest period of the ranch horses.”

Studying Working Ranch Horses in Brazil

Trindade and his fellow researchers observed 14 mixed breed ranch horses working on two Brazilian beef farms on seven summer days. Before and after work on each of the study days, they carried out 10 five-minute video recordings of each horse—one of his facial expressions and one of his body language—at five time points each. The scientists made these recordings 14 hours and about one hour before work, then again immediately after, six hours after, and 12 hours after work.

The horses also wore heart monitors and GPS trackers throughout the workday. After work, the researchers drew blood to analyze markers of tiredness (lactate, creatine kinase, and aspartate aminotransferase) at critical time intervals, and they evaluated the horses’ gaits in subjective lameness exams.

Later, they ran 30-second video clips through an analytical software program to acquire objective, measurable data about the horses’ facial and body movements.

They found that the horses worked an average of four hours per day, covering nearly 19 kilometers (12 miles) at an average speed of 5.4 kilometers/hour (3.3 mph), Trinidade said

Body Language Specific to Tiredness

The researchers noted certain facial expression changes after work compared to before, including partially closed eyes, raised nostrils, and increased lip movement. However, it was critical that they distinguish facial expressions of pain from those of tiredness, said Trinidade. Raised nostrils and more lip movement indicate tiredness but might also result from mouth pain due to bit use and/or a dry mouth, he said.

Therefore, horses’ overall body language seemed more likely to represent their state of fatigue, Trinidade explained. Specifically, the researchers saw an increase in resting body language, including a “decrease in attention to the surroundings and movements to avoid flies after a workday that could be attributed to the horses’ earlier aerobic effort.”

When they compared their observations to their laboratory testing and physical data, the team found a link between weight-shifting and workload. This might be the most useful indicator in the field for revealing the level of tiredness, Trinidade said.

“I recommend that workers or riders watch their horses after an exercise session,” he said. “If they shift their weight between forelimbs more than once per minute, it may mean a certain degree of physical tiredness.” Handlers could monitor weight-shifting for patterns that suggest increasing fatigue, he added.

Preventing Tiredness From Becoming Exhaustion

None of the horses in the study appeared to have behavioral or physiological signs of extreme fatigue or exhaustion, Trinidade said. Even so, this large horse population is at risk of being overworked.

In Brazil, more than 70% of the country’s five million horses work on cattle ranches. Farmers largely prefer this 400-year-old tradition over machine work for technical and financial reasons, said Trindade. “However, these are the horses that receive the least care,” he said. “Because of this, I classify them as a ‘huge invisible herd.’”

Certainly, working horses will experience tiredness, just as their working riders do, which in and of itself is not a concern, Trinidade said. The issue is when tiredness turns into exhaustion.

“Any exercise will interrupt the horse’s homeostasis, so physical tiredness is expected to happen after any physical activity,” he explained. “However, it is important to know the degree of tiredness that the horses suffered, as this directly affects their level of welfare. It is absolutely not desirable for horses to finish the workday exhausted. So, the first step in our work was to identify indicators related with physical tiredness on horses.”

Finding inexpensive, easy-to-recognize indicators of welfare compromise could help improve quality of life for these horses, Trindade said. “Ranch horses must not be seen as instruments of work but rather as sentient beings,” he told The Horse.