Five million horses live in Brazil. Nearly three-quarters of them work as ranch horses on beef cattle farms, spending long days driving, cutting, and transporting, sometimes across difficult terrains and in extreme weather. Researchers are helping ranchers recognise the signs of physical tiredness to prevent exhaustion.

It can be a hard life. And at the end of the day, they wear their fatigue on their faces.

According to equine behaviour researchers, though, these facial expressions combined with the horses’ general body language can lead to useful, concrete indicators telling their handlers if they’re reaching the limits of physical exhaustion.

“We expect to see physical tiredness after any physical activity, but it’s important to know the degree of tiredness that the horses have suffered, as this directly affects their welfare,” said Pedro Henrique Esteves Trindade, PhD candidate at São Paulo State University, in Jaboticabal, Brazil.

Trindade and his fellow researchers observed Brazilian ranch horses before and after work over a seven-day period, making video recordings of their behaviour and noting more than 50 different behaviour variables. They also monitored their heart rate and took blood samples.

The 14 crossbred horses, ranging in age from 6 to 27, included 13 geldings and one mare. They lived and worked on two commercial beef farms in São Paulo State, known for its “gently sloping terrains.” By day, the animals worked in pairs or groups, and by night they rested and grazed in grass pastures in groups (with feed compliments). All the horses were fit with good body condition, and none wore shoes, he said.

Although the horses covered an average of nearly 19 km in a single day, very few of the body language parameters changed from before work to after work, Trindade said. That might be because, even though they worked as many as eight hours, the intensity was relatively low since they kept fairly low speeds.

Still, they did note that, after work, the horses kept their eyes partially closed longer and more often, tightened their mouths more, shifted weight between the front legs more, and spent more time standing on three legs instead of four, he said. They also held their ears forward less often, showed the whites of their eyes less, spent less time turning their heads left or right, and generally made fewer movements in reaction to flies.

These behaviours suggest the horses were “tired,” but they could also be signs of pain, as scientists have noted similar body language in horses just after castration, Trindade said. The  creatinine kinase (CK) levels in the studied horses were also fairly elevated after a day’s work, pointing to possible soreness. Still, their heart rates dropped significantly shortly after work, meaning they were recovering from the exercise.

recognising fatigue in ranch horses

Still images from 30-s video clips of two ranch horses (A and B) pre- and post-workday.  The images show both ranch horses orienting their ears forward and backward before and after workday, respectively. Horse A has its eye partially closed (A, post-workday), while horse B has its eye fully closed and is showing contraction of the eyelid post-workday. Horse A showed contraction of the inner brow raiser before and after the workday, and showed tension of the muzzle and mimic muscles post-workday. Horse B showed nostril lift before workday. See Table 2 (in original paper) for descriptions of the categories of facial expressions. Image source:

But that doesn’t mean it didn’t leave them with pain somewhere, he added. In particular, they might have had pain in the mouth area (from the rider pulling at the bit) or in the musculoskeletal system, from the effort. “This increase in the CK activity and the facial tension post-workday could nevertheless be interpreted as low level pain induced by transitory changes in sarcolemma permeability, that did not produce lameness,” Trindade and his colleagues stated in their study.

“Now science needs to test these indicators and establish classifications of intensity of physical tiredness using dose-response studies,” Trindade said in an interview. “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.”

“Effect of work on body language of ranch horses in BrazilEffect of work on body language of ranch horses in Brazil, by Pedro Henrique Esteves Trindade,
Elke Hartmann, Linda J. Keeling, Pia Haubro Andersen, Guilherme de Camargo Ferraz, Mateus José Rodrigues Paranhos da Costa is published in Plos One. It is open access and can be found here.