Cases of equine metabolic syndrome (EMS) are on the rise, and research sponsored by Morris Animal Foundation is helping to unravel the complexities of EMS.

The term “equine metabolic syndrome” was coined in 2002. It was used to describe a disease that shared many features with metabolic syndrome in people. In horses, the syndrome is characterized by obesity (either generalized or regional), insulin resistance and a predisposition to laminitis.

The rise in EMS cases coincided with the transition of horses from working animals to companion animals with more sedentary lifestyles. But EMS is a complex disease that involves more than just lifestyle, and has both genetic and environmental components. This complexity has complicated EMS research, though new breakthroughs could provide key clues toward treating this disease.

Morris Animal Foundation is a major sponsor of EMS research around the world, and our grantees are leaders in the field. We’re excited about some recent findings from our funded grants.

Genetics play a role in EMS

A genetic explanation for this disease makes evolutionary sense and supports what we see clinically. It was beneficial for early equids to develop an efficient metabolism to survive in times of scarce resources. However, this same trend toward thriftiness can lead to obesity and insulin dysregulation.

Researchers at the University of Minnesota published findings on a correlation between height in Welsh ponies and their baseline insulin levels. They found that shorter ponies had higher baseline levels, which translates into a greater potential for EMS. ¹

Data on the predisposition of certain horse breeds for developing EMS provides further evidence for a significant genetic influence. The Minnesota team also published a study that estimated the heritability of certain EMS biochemical traits in Morgan and Welsh ponies, which ranged from moderate to high heritability. The findings have implications for future research on genetic risk factors for EMS.²

And so does the environment

The University of Minnesota research team is also investigating environmental factors. Although it’s tempting to give genetics the major role in the development of EMS, some experts suggest that almost 50% of the phenotypic variability in EMS is due to environmental factors.

The Minnesota team recently reported how endocrine-disrupting chemicals could play a role in clinical disease in horses. They reported that horses living close to federal Superfund sites, where endocrine-disrupting chemicals may be concentrated, were more likely to have a history of laminitis and biochemical abnormalities related to EMS.³ Diet, exercise and season can also influence the EMS phenotype, but research has shown that these factors account for only a small part of this variation.

New research focus areas

Morris Animal Foundation has several new studies in progress that are tackling EMS from different directions.
Recently funded projects include:

• How the gut microbiome and metabolome influence insulin levels
• A description of the microbiome in Shetland ponies who do and don’t develop EMS
• The effect of phenylbutazone on insulin and glucose dynamics
• The roles of adiponectin and systemic inflammation on insulin dysregulation.

EMS is a complex disease. Through strategic funding, Morris Animal Foundation hopes to generate a path to better diagnostics, treatments and, hopefully, new
preventive strategies for this serious threat to horses. Learn more at morrisanimalfoundation.org.

References

¹Norton EM, Avila F, Schultz NE, Mickelson JR, Geor RJ, McCue ME. “Evaluation of an HMGA2 variant for pleiotropic effects on height and metabolic traits in ponies”. J Vet Intern Med. 2019;1–11. https://doi.o r g /10 .1111/ j v i m .15 4 03

2Norton EM, Schultz NE, Rendahl AK, McFarlane D, Geor RJ, Mickelson JR, McCue ME. “Heritability of metabolic traits associated with equine metabolic syndrome in Welsh ponies and Morgan horses”. Equine Vet J. 2019;475-480. h t t p s : //d o i . o r g /10 .1111/e v j .13 0 53

³Durward-Akhurst SA, Schultz NE, Norton EM, Rendahl AK, Besselink H, Behnisch PA, Brouwer A, Geor RJ, Mickelson JR, McCue ME. “Associations between endocrine disrupting chemicals and equine metabolic syndrome phenotypes”. Chemosphere. 2019;652-661. https://doi.org/10.1016/j.c h e m o s p h e re. 2 018 .11.13 6