Fat horses face health problems
By Christy Jackson, Virginia-Maryland Regional College of Veterinary Medicine
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The increase in obesity among humans has alarmed physicians and public health officials, and veterinarians have remarked on a similar trend for dogs and cats. A team of researchers in the College of Agriculture and Life Sciences (CALS) and the Virginia-Maryland Regional College of Veterinary Medicine (VMRCVM) at Virginia Tech has documented that horses also face serious health risks because of obesity.
Fifty-one percent of the horses evaluated at more than 114 farms were determined to be overweight or obese — and may be subject to such serious health problems as excess blood insulin and a particularly debilitating cause of lameness called laminitis, also known as founder.
“This study documents that an extremely important problem in horses has been under-reported,” says Dr. Craig Thatcher, professor in the VMRCVM’s Department of Large Animal Clinical Sciences (DLACS).
“Obesity, over the past decade, has become a major health concern in horses,” says Dr. Scott Pleasant, associate professor in DLACS. He had seen laminitis in obese horses when he was in private practice, but it was a special mare brought to the Virginia Tech clinic that provided impetus for the study.
“In the fall of 2005, we had a horse brought to the Veterinary Teaching Hospital for treatment of severe laminitis. She ended up sloughing both of her front hooves. Avatara, a 12-yearold Lipizanner mare, was a wonderful horse owned by kind and committed people,” says Pleasant.
“Laminitis is a failure of the connective tissue bond between the horse’s hoof and the bone within the hoof,” explains Pleasant. “When that bond fails, and the hoof and bone begin to separate, it is horribly painful for the horse. Laminitis is one of the most devastating and debilitating problems that we see with the horse.”
The faculty and students at the Veterinary Teaching Hospital worked long and hard, and, against almost insurmountable odds, Avatara survived.
“After witnessing what Avatara went through, we wanted to know what happened and how to prevent it,” says Pleasant. “Avatara’s owners invited us to their farm to assess their other horses. Dr. Thatcher, who is a nutritionist, and I went on the consult. We found that all of the horses on the farm were overweight and that they were eating only pasture.
“The fact that horses can become overweight just from grazing pasture emphasized why obesity is becoming a serious problem for the horse industry,” says Pleasant. “We decided to define the scope of the problem as the first step.”
After surveying the academic literature, the researchers discovered that only one documented study on the incidence of equine obesity existed, according to Thatcher. It was an ownerreported survey done in 1998 by the National Animal Health Monitoring System (NAHMS) through the United States Department of Agriculture. This study reported the prevalence of overweight or obese horses to be 5 percent.
However, based on the horses seen routinely in clinical practice at Virginia Tech, the research team hypothesized the prevalence of overweight and obese horses was much higher. “We thought it was at least 15 percent,” says Thatcher.
Pleasant and Thatcher collaborated with Dr. Ray Geor, the Paul Mellon Distinguished Professor of Agriculture, and epidemiologist Dr. Francois Elvinger, associate professor in DLACS, to design a study.
Geor, a veterinarian and exercise scientist, is the director of the Middleburg Agricultural Research and Extension (MARE) Center, where research on obesity, insulin resistance, pasture-associated laminitis, and other health issues in horses has been ongoing since the early 1990s. He approached the Virginia Horse Industry Board to fund a pilot study.
“And Dr. Elvinger helped design the study so our observations could come to real conclusions,” says Pleasant.
The study hypothesized that overweight horses may suffer from insulin and sugar imbalances, chronic inflammation, and oxidative stress, a malady that occurs as a result of changes to metabolic processes that alter the delicate balances between the destruction and creation of new cells in the body.
“Oxidative stress is an imbalance between the production of free radicals and reactive oxygen species and the body’s antioxidant defense mechanisms, and that imbalance is in favor of the oxidants,” says Thatcher. “Those free radicals and reactive oxidant species can affect macromolecules in the body, such as lipids, DNA, and proteins, ultimately causing cell death or changing the functionality of these macro-molecules.”
The researchers spent two months during the summer of 2006 measuring 300 horses and assessing their blood. When the results were tabulated, prevalence of overweight and obesity turned out to be close to 20 percent, with high incidence of insulin resistance.
Pasture problem
The study documents that equine obesity can result from natural grazing behavior, which defies conventional thinking that blamed overweight on overfeeding with grains and other feed supplements. The majority of horses examined were fed primarily pasture and hay with very little grain and concentrate.
The evidence indicates that improved forage is a common contributing factor in equine obesity. Thatcher believes this may result from many pasture forages having been fortified to improve weight gain and productivity of cattle and other food animals, with little thought given to how these forages might affect horses.
“Pasture species developed for livestock have more energy and carbohydrates,” agrees Geor.
By studying herds with a high incidence of laminitis problems, Geor and his colleagues noticed that not all the animals became overweight and at risk for insulin-related problems. “Diet is an important factor, but susceptibility to obesity and laminitis is more than just overeating on a rich pasture,” he says. “We have found that insulin resistance and a tendency to accumulate fat over the neck (cresty neck) are key factors, problems that are magnified when these animals are given access to high-energy forages.”
So the researchers are now looking at genetics and metabolism to better understand what underlies this susceptibility to weight gain and laminitis.
“Some horses are easy keepers — they appear to thrive on very little feed,” says Geor. “Some breeds are probably more predisposed to being overweight than others. Ponies are by far the best example of that.”
New pasture studies are focusing on the role of hormone levels, oxidative stress, inflammatory biomarkers, and antioxidant mechanisms. “In collaboration with Chris Teutsch at the Southern Piedmont Agricultural Research and Extension Center, we are evaluating the nutrient profiles of different types of grasses harvested at different stages of maturity or growth to determine optimum forage types and harvesting stages to aid in the management of equine obesity,” says Pleasant.
Teutsch, associate professor of crop and soil environmental sciences, conducts research in the area of forage management. He has reported, for instance, that high levels of legumes can contribute to laminitis. Many Virginia pastures contain white clover, so that is one species that would not need to be added to a pasture mix.
In the new research, Teutsch, Pleasant, Thatcher, and Geor have completed one season looking at carbohydrates at different growth stages in two grasses. “We are looking at orchard grass, which is a cool-season grass, and Bermuda grass, which is a warm-season grass,” says Teutsch. “Both of these species are used for horse hay. We are still in the process of having the grasses analyzed at a lab that is fine-tuning the analysis to distinguish between types of carbohydrates,” he says.
“We are looking for nutrient profiles of pasture grasses and hay that would not encourage weight gain in companion and light performance horses,” says Pleasant.
MARE Center researchers are also looking at seasonal and daily dynamics in pastures. “We are looking at the carbohydrate profile of the pasture species and how that impacts metabolism — especially the blood insulin response because this is linked to laminitis risk,” says Geor.
Exercise problem
In addition to diet, the majority of the horses studied were under-exercised. They were left on pastures to eat, but did not have a regular exercise regimen.
Horses today are managed much differently from their evolutionary roots, says Pleasant. “The horse evolved as a freeroaming grazer on sparse pasture types,” he says. Later the horse was a work animal, serving as a source of transportation and draft power. Today, most horses are companions and light performance animals, being worked less than three times a week, he says.
“We can see with increased nutrition and lack of exercise how horses could drift toward being overweight,” Pleasant says.
In a new research project, Dr. Jill McCutcheon, professor of biomedical sciences and pathobiology, is leading a project to determine the effect of exercise. McCutcheon is based at the Marion duPont Scott Equine Medical Center in Leesburg but is using the MARE Center’s overweight Arabian horses for the study. Geor calls the collaborative project “practical research that will help us provide recommendations.” The U.S. Equestrian Federation is funding the study, which will “apply a reasonable level of structured exercise to the horse’s daily life,” says Geor. “We are asking, ‘What does that do to reduce obesity, improve insulin sensitivity, and lower the risk for disease?’ We will compare different levels of exercise and try to figure out what works best.”
Recommendations
Although research is ongoing, based on what they know and what they suspect, the researchers can make some suggestions for horse owners.
“The most important thing that horse owners can do is to regularly assess their horse’s body condition and then adjust the horse’s diet accordingly,” says Pleasant. “Body condition scoring (BCS) is a technique that evaluates the accumulation of fat over specific regions of the body and is therefore more appropriate for evaluating obesity than weight. Using an accepted 1 to 9 body condition scoring system, scores 4-6 represent optimal body condition. “With a little bit of education, owners can learn body condition scoring and do it without help,” Pleasant says.
BCS works by assessing fat both visually and by palpation, or touch, in six areas on the horse: the neck, over the withers, behind the shoulder, over the ribs, along the top line or back, and around the tail head. A numerical value is assigned based on the fat assessment in all six areas.
Geor agrees that close monitoring and management of horses and ponies susceptible to weight gain is crucial for prevention of problems, such as laminitis. This includes close attention to diet and in some cases restricted access to pasture. “Sugars in feed and forage cause insulin in the blood to go up and that response is magnified in overweight, easy keeper animals. Current evidence suggests that these disturbances in insulin response can contribute to development of laminitis. The sugar content in Virginia pastures in April and May tends to be high, so those horses most at risk should be off pasture then.”
There are companies around the country that will test pasture clippings and hay for carbohydrate content. This information can guide selection of hay for the portly horse or pony. But, Geor says, “We need more information on how the different kinds of carbohydrates, such as sugars, starches, fructans, and fiber, impact metabolism. Results of our research should provide this information, which will better guide feeding recommendations.”
Human health may also benefit from the study of metabolic changes in horses, such as insulin resistance and inflammation, says Thatcher. “Humans suffering from obesity experience chronic inflammation. If obese horses are found to suffer from chronic inflammation, the possibility would then exist for the horse to serve as an animal model for the study of obesity in people.”
