If your horse is cold, rug him. The trick, though, is to know if he really is cold. Unfortunately, humans (and even equine scientists themselves) aren’t necessarily very good at picking up the signs that our horses are too hot, according to a recent study. Using a commercial sensor can help alert us of overheating in rugged horses, helping us improve their health and welfare.
“Our data picked up changes in humidity under the rug indicating the horses were sweating, although we ourselves didn’t feel the sweat, so that was quite a shock actually,” said Ella Bartlett, MSc candidate at the University Centre Sparsholt, Winchester, in Hampshire, the U.K. Bartlett presented a study validating the use of the Orscana Sensor to detect under-rug temperatures during the 14th Conference of the International Society for Equitation Science (ISES), held in Rome, Italy.
“As humans, we aren’t that good at feeling our horses’ sweat,” Bartlett said during her presentation. “All the horses in our study were starting to sweat a lot earlier than we thought they were. Maybe we need to consider alternative methods because we aren’t that sensitive to these changes.”
Bartlett and her fellow researchers, including David Marlin, PhD, a scientific consultant in Cambridge, England, studied six riding horses rugged in winter (November and December in the U.K.).
To make the horses gradually hotter, the scientists added additional rugs to the horses every hour. For measurement purposes, they fitted each horse with two kinds of equipment: a commercially available monitor (the Orscana Sensor) measuring temperature and humidity, and a research data logger (an “iButton”) that takes temperature readings every minute.
The research team also registered environmental factors like temperature and relative humidity, and they observed each horses’ behaviour via video recordings.
Finally, to compare with the way humans would generally check their rugged horses’ comfort, they also carried out subjective exams of the horses, looking at them, feeling under the rugs, and taking rectal temperature and respiratory rates to get an idea of how the horse was faring.
They found that the commercial sensor and the research data tool gave similar information about the horses’ increasing body temperature, Bartlett said. However, this data wasn’t consistent with the ‘owner’ exams—indicating that even skilled horsemen don’t necessarily pick up on the cues that a horse is getting too hot.
“No behaviours were shown that were connected to the horses being uncomfortable, although the data indicated that they may have been,” Bartlett explained. “And rectal temperature and respiratory rates remained unchanged.”
What’s more, they found that sweating increased significantly, and at a much faster rate than it appeared without the use of technology, she added.
“Clear inflection points were identified when horse humidity and temperature was plotted against one another, highlighting an increase in under-rug humidity that consistently occurred around 25 degrees,” Bartlett said. “This is reported to be the upper limit of the equine thermoneutral zone (i.e. the point where we would expect horses to start sweating, to maintain thermal homeostasis).”
“From 25 degrees onwards, moisture was being added under the rugs as temperature increased,” Bartlett explained. “At first we thought maybe it was from moisture in the air, but that would have been linear (increasing gradually from the start), and that was not the case. The horses were most likely sweating but at a level undetectable by traditional methods.”
An overheated horse is one whose body temperature is exceeding what is known as his ‘thermoneutral zone (TNZ).’ The TNZ encompasses a range of ambient (environmental) temperatures that don’t require an animal (or human) to expend energy in order to stay cool (or warm).
The TNZ can vary significantly from one species to another. For example, in horses, the range is from 0 to 25 degrees Celsius. But in (nude) humans, 25 degrees is the starting point: their range extends from 25 to 30 degrees without clothing.
“It’s so much higher and narrower than for horses, so that’s why we recommend that horse owners don’t select their horses’ rugs based on how they themselves feel at the given temperature,” Bartlett told Horses and People.
Using a sensor takes out the guesswork – especially since human guesswork appears to be fairly inaccurate when it comes to a horse’s body temperature, she explained. The commercial sensor includes an alert feature that warns owners that the horse is reaching a threshold of being uncomfortable, according to Bartlett. That feature is useful, she said, as it’s better at picking up signs of overheating than humans are.
“The use of this tool could be beneficial in guiding rug selection based on individual requirements,” she said.
The sensor requires the use of a rug (to attach it), and for the moment has only been tested in stabled horses. However, research in pastured horses is currently in progress, Bartlett said.
For details on the factors that can influence a horse’s need for rug cover, owners can consult Marlin’s advice in this article.