Page 91 - May 2022

sweat efficiently and don’t lose as much
fluid and electrolytes as an unconditioned overweight horse. Fit horses can keep going for miles or exert strenuously for a race and keep within a normal range of body temperature.
WHICH HORSES ARE AT RISK?
There are very few risk factors regarding which horses are more susceptible—in terms of breed, color, gender, age or where they are born. It doesn’t seem to make a difference whether
a horse is born into a hot climate or not. “The only association that’s been found is a genetic component. This is based on early research done here in Florida, published in 2011. We have now done additional investigation, collaborating with a researcher (Dr. Samantha Brooks) at the University of Florida,” says Mallicote.
“Beyond individual genetic connections, not much else has been identified as risk factors. There are, however, no reports of anhidrosis in Arabian horses. There may be a few that have experienced this problem, but it’s not been reported in the literature.” This may be due
to their evolution in a hot country; they may have some natural adaptation to heat and more resistance to this problem than other horses.
“Prevalence is hard to accurately identify because of the effect of climate. But here in Florida, we find somewhere between 2 and 6% of horses affected. Reports from Pakistan state that as many as 13% of horses are affected. It’s difficult to put together the regional aspects and come up with a meaningful figure, but
it’s a common problem in this type of
climate,” she says.
Small horses and young horses
may not
be as
unless you move him to a hot, humid climate. Some horses seem more prone to develop anhidrosis. “It seems to occur in all breeds, but I’ve never seen an Arab with this problem,” says Randall. “I’ve seen anhidrosis in a number of endurance horses but never had to treat an Arab for this; it’s mostly been Quarter Horses and a few Friesians.” The Friesians originated in a northern, cooler climate and have a lot of body mass, which makes it harder to dissipate heat.
“Dark colored horses seem more at risk. Any horses with a lot of muscle mass, like Quarter Horses, are affected severely if they develop anhidrosis,” says Randall.
“There is also an association between use of antihistamines and anhidrosis, but we don’t know if the antihistamine is a direct cause of non-sweating or because whatever mechanism is
causing these horses to not sweat is somehow associated with the allergic problem and the
need for antihistamines,” says Randall. There is also an association with
certain antimicrobial drugs that are sometimes used in
foals with Rhodococcus equi pneumonia. “Foals tend to
have a problem in hot weather
“Dark colored horses seem more at risk. Any horses with a lot of muscle mass, like Quarter Horses, are affected severely if they develop anhidrosis.”
– Dr. Matt Randall
There were no reports of anhidrosis in Arabian horses in a 2011 study performed in Florida, perhaps because of their evolution in a hot country.
SPEEDHORSE May 2022 89
adversely affected. Their smaller bodies are more efficient at getting rid of body heat and they are usually not exerting as much in hot weather like an adult horse in training or one with an athletic performance career. A larger animal has a larger volume-to-surface area and holds more heat; a large, heavy horse will overheat more quickly than a small one.
“The less severe cases, if they are out at pasture and not working, and are able to maintain a safe body temperature in their environment, might not be identified. We
do see some severe cases in which the horses can’t tolerate being outdoors in the heat. They will stand in a shady place in the pasture and still can’t cool themselves enough. The less-severely affected animals may be able to tolerate the heat, unless they are being asked to work,” says Mallicote.
A horse genetically prone to anhidrosis may never have problems in a cool climate,
Small horses and young horses, who are efficient at getting rid of body heat, are usually not exerting as much in hot weather compared to an adult horse in training or one with an athletic performance career.
EQUINE HEALTH
Horses that are fit and in good condition sweat efficiently and don’t lose as much fluid and electrolytes as an unconditioned overweight horse.
Beside genetic connections, not much else has been identified as a risk factor for anhidrosis.