Researchers compare metabolic syndromes in horses, humans and dairy cows

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A 7-year-old Romanian Draft Horse mare with physical characteristics of equine metabolic syndrome. Photo: Author's private collection
A 7-year-old Romanian Draft Horse mare with physical characteristics of equine metabolic syndrome. Photo: Author’s private collection

Important differences between obesity-related metabolic problems in humans, horses and dairy cows have been cited by researchers in a just-published review.

Zsofia Daradics and her fellow researchers, writing in the journal Life, said obesity had become a serious health problem in human and animal populations.

“It is estimated that it may affect over 85% of the human population and 70 to 80% of horses and cows by 2030,” they said.

Fat cow syndrome is a combination of metabolic, digestive, infectious, and reproductive disorders that affects obese dairy cows around calving. It occurs most frequently in loose-housing systems, where cows are managed in one group, disregarding their lactation stage.

Equine metabolic syndrome in horses was named after human metabolic syndrome and has insulin dysregulation as a central and consistent feature. It is often associated with obesity, although it may occur in lean horses as well.

Other inconsistent features of equine metabolic syndrome are cardiovascular changes and fat dysregulation. Laminitis is the main clinical consequence.

The researchers said human metabolic syndrome holds a 30-year lead in research and represents a clustering of risk factors that comprise abdominal obesity, an abnormal level of cholesterol and other lipids, high blood pressure, and elevated blood sugar, which are associated with a higher risk of cardiovascular disease, and a five-fold increased risk for type 2 diabetes.

Divergent growth rings in the hoof of the same 7-year-old Romanian Draft Horse, indicating laminitis. Photo: Author's private collection
Divergent growth rings in the hoof of the same 7-year-old Romanian Draft Horse, indicating laminitis. Photo: Author’s private collection

The review team investigated previously published research in a bid to develop a better understanding of the underlying mechanisms of obesity-related metabolic dysfunction in animals, especially cows and horses, in comparison with human metabolic syndrome.

They traversed the circumstances that appear to drive the metabolic syndrome in the different species.

The authors noted that the term equine metabolic syndrome was first defined in 2002 as an association of obesity, insulin dysregulation and laminitis.

Later, in 2010, the American College of Veterinary Internal Medicine published a consensus statement, and included other factors, including fat deposits in specific locations or general obesity, insulin resistance and a predisposition towards laminitis.

Additional conditions were blood lipid problems, high blood pressure, altered reproductive cycling in mares, and increased systemic markers of inflammation.

In 2019, the European College of Equine Internal Medicine delivered an up-to-date consensus on the syndrome, saying that this cluster of risk factors holds insulin dysregulation as a central hallmark, where hyperinsulinemia is the most important feature.

Spiking insulin levels following meals is an important feature of insulin dysregulation in horses, they said. Decreased clearance of insulin by the liver might also provoke hyperinsulinemia, especially in horses with obesity and insulin resistance, since more than 70% of the insulin secreted by the pancreas is normally cleared by the liver.

Field-based observations highlight that hyperinsulinemia can trigger laminitis in horses.

The authors said human metabolic syndrome differs from the equine disease in several material ways. The most important problems that arise in humans are type 2 diabetes and cardiovascular disease, while in horses it is laminitis.

“In both humans and equids, a high energy diet combined with sedentary lifestyle have resulted in obesity and metabolic disturbances,” they said.

In both species, the adipose tissue not only serves as fat storage, but also has endocrine functions. The fat tissue produces adipokines and releases inflammatory mediators and pro-inflammatory cytokines.

“Though mechanisms behind these processes are less documented in equids as compared to humans, the adipose tissue inflammation that affects metabolic and biochemical processes show similarities between both species.”

In humans, insulin resistance induces increased secretion of insulin by the pancreas to regulate glucose concentrations in blood. Conversely, horses with metabolic syndrome have compensated hyperinsulinemia.

“The development of hyperinsulinemia in horses is highly dependent on dietary composition, which is an important factor in the development and management of human metabolic syndrome as well.”

Type 2 diabetes is a major problem in people with metabolic syndrome, but is less likely in equids, although horses may also develop diabetes in some cases.

In humans, the most common risk factors associated with type 2 diabetes are a family history of diabetes, high blood pressure, impaired glucose tolerance, being overweight, physical inactivity, ethnicity, and poor nutrition during pregnancy. Risk factors in horses include metabolic syndrome and pituitary pars intermedia dysfunction (equine Cushing’s diseases), but available scientific evidence is scarce.

In conclusion, the review team found that metabolic syndrome in humans differed in several aspects from both the cow and equine disease.

“The most important pathological factor is the affliction of the cardiovascular system in humans; fatty liver in cows; and the development of laminitis in horses,” they said.

“The mechanisms that lead to these potentially life-limiting consequences are not fully comparable, although the changes in these species take place in the vascular system.”

Inflammatory conditions in fat tissue, and the effects on metabolic and biochemical processes show similarities between all species, they said.

There were still many underlying mechanisms of metabolic syndrome which have not been scientifically explored, they noted. “Therefore, the current comparative approach might serve as a starting point for future investigations and improvements in this field.”

The review team comprised Daradics, Cristian Crecan, Mirela Rus, Iancu Morar, Mircea Mircean, Andra Diana Cecan and Cornel Cătoi, all with the University of Agricultural Sciences and Veterinary Medicine in Cluj-Napoca, Romania; and Adriana Florinela Cătoi, with the University of Medicine and Pharmacy, also in Cluj-Napoca.

Daradics, Z.; Crecan, C.M.; Rus, M.A.; Morar, I.A.; Mircean, M.V.; Cătoi, A.F.; Cecan, A.D.; Cătoi, C. Obesity-Related Metabolic Dysfunction in Dairy Cows and Horses: Comparison to Human Metabolic Syndrome. Life 2021, 11, 1406. https://doi.org/10.3390/life11121406

The study, published under a Creative Commons License, can be read here

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