New Study: Equine Obesity More Prevalent than Previously Reported

A team of researchers in the Virginia-Maryland Regional College of Veterinary Medicine and the College of Agriculture and Life Sciences at Virginia Tech have determined that horses are facing serious health risks because of obesity.

Of the 300 horses examined, 51% were determined to be overweight or obese, and could be subject to serious health problems like laminitis and hyperinsulinemia as a result. And, just like people, it appears as though the culprits are over eating and lack of exercise.

"This study documented that this is an extremely important problem in horses that has been under-reported," said Craig Thatcher, DVM, PhD, Dipl. ACVN, a professor in the veterinary college's Department of Large Animal Clinical Sciences.

Thatcher and his colleagues believe the study results suggest that horse owners should change some of the ways in which they care for their horses--and hinted that horses could emerge as an important model for studying the health implications of human obesity.

"Obesity, over the past decade, has become a major health concern in horses," said Scott Pleasant, DVM, MS, Dipl. ACVS, an associate professor in Department of Large Animal Clinical Sciences. "This is primarily because of its association with problems such as insulin resistance and laminitis."

In fact, it was a spike in pasture-associated laminitis cases that led Pleasant to grow curious and seek the collaboration of Thatcher, an internationally renowned veterinary nutritionist, on the innovative research project. Ray Geor, MVSc, PhD, Dipl. ACVIM, the Paul Mellon distinguished professor of agriculture in the College of Agriculture and Life Sciences, and director of the Middleburg Agricultural Research and Extension Center in Middleburg, Va., and Francois Elvinger, DrMedVet, PhD, Dipl. ACVPM, an epidemiologist and associate professor in the Department of Large Animal Clinical Sciences, also worked on the study.

Funded in part by the Virginia Horse Industry Board, the researchers hypothesized that overweight horses might 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.

Other problems caused by equine obesity are heat stress, increased bone, tendon, and joint injuries, and reduced performance levels.

Until now, only one other study had looked at obesity in horses. A 1998 owner-reported survey of horse owners conducted by the USDA's National Animal Health Monitoring System (NAHMS) suggested about 5% of horses were overweight.

Based upon the horses routinely seen through clinical practice in the Veterinary Teaching Hospital, however, the researchers suspected the incidence might be higher. "We thought it was at a level of at least 15%," said Thatcher.

The research team designed a prospective study and examined 300 horses from 114 different farms chosen randomly from about 1,000 horses that have been treated through the college's Equine Field Service program.

Two independent body-conditioning scores (BCS), which assess the amount of fat cover on the horses, were assigned to each animal. Each horse was checked for signs of laminitis and blood was drawn to assess glucose and insulin levels as well as other hormones, cytokines, and oxidative biomarkers

While laboratory testing and data analysis are still underway, the research team has already made some alarming discoveries.

Of the horses in the study, 51% were found to be overweight and 19% were found to be obese. Eighteen percent of the overweight horses and 32% of the obese horses were hyperinsulemic.

The study results also suggested that equine obesity might result from natural grazing behavior instead of the overfeeding of grains and other feed supplements--which defies conventional thinking on equine weight matters. The majority of horses examined in the study were fed primarily pasture and hay with very little grain and concentrate.

Instead of overfeeding of grain and concentrates, the evidence indicated that improved forage and lack of exercise are the two most common contributing factors in equine obesity.

Horses today are managed much differently from their evolutionary roots, indicated Pleasant.

"The horse evolved as a free-roaming grazer on sparse pasture types," he said. Later, the horse served primarily as a work animal, serving as a source of transportation and draft power. Today, most horses serve as companions and light performance animals, he said.

This research project is ongoing and has laid the groundwork for a series of provocative new studies.

"Other studies by our group have clearly shown that obesity and insulin resistance are important risk factors for pasture-associated laminitis," said Geor. "This study underscores the importance of obesity to equine health."

Geor noted that current studies are further exploring how obesity, diet and exercise management alter insulin resistance and therefore the susceptibility of horses and ponies to laminitis. The goal is development of management strategies that assist in the avoidance of this devastating disease.

The researchers are now focusing on the role of hormone levels, oxidative stress, inflammatory biomarkers, and antioxidant mechanisms.

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