Obesity is on the rise, not only in humans and companion animals, but also in our beloved horses and ponies. In humans, dogs and cats, we hear the term diabetes mellitus; however, in the horse it is very rare to develop diabetes. Instead, equids of all ages can develop Equine Metabolic Syndrome (EMS).
EMS is composed of three characteristics. First, the consistent feature of EMS animals is that they demonstrate insulin dysregulation (ID), a collective term for both tissue insulin resistance and basal/postprandial hyperinsulinemia. This means that typically the concentrations of insulin in the blood are higher than what’s considered normal either before and/or after eating feeds and forages especially those rich in starch and/or sugar. Second, there is an increased risk of developing endocrinopathic laminitis, which is laminitis resulting from hormonal (in particular insulin) disturbances rather than in association for example with severe infection (sepsis) or certain intestinal conditions. Finally, most, but not all, EMS animals show increased general or regional adiposity meaning that many are overweight or more typically obese.
The main risk factor for endocrinopathic laminitis is now believed to be insulin dysregulation although the exact link between abnormally high circulating insulin concentrations and the development of laminitis is not known. However, it does mean that what we feed our horses may directly impact their risk for endocrinopathic laminitis. Unfortunately, limited work has been undertaken in the EMS/ID horse and our current recommendations were largely derived from horses that suffered from polysaccharide storage myopathy (PSSM), a very different condition. Thus, we set out to explore and, help define nutritional recommendations for EMS/ID horses and thereby improve their welfare.
In our recent publication1 in the Equine Veterinary Journal, carried out in collaboration with Pat Harris, MA PhD VetMB DipECVCN MRCVS, head of the Equine Studies group at the Waltham Petcare Science Institute, we fed various feedstuffs to EMS/ID horses as well as healthy horses in two separate studies.
Currently, it is typically recommended that EMS/ID horses are fed low sugar and starch feeds and forages that contain <10-12% non-structural carbohydrates (NSC i.e. starch and water soluble carbohydrates) on a dry matter basis with an appropriate ration balancer. In our first study, various feeds with different levels of protein and NSC were fed in a cross-over study to both ID and non-ID horses. The results of this study showed that, even when fed low amounts (~1g/kg BW) of certain feeds that did not provoke any insulin response in Non ID horses, exaggerated insulin responses may occur in ID animals confirming the need to undertake work specifically in such individuals. In addition, the study suggested that non-structural carbohydrates were the main driver behind the post-meal insulin response rather than protein in the ID horse. In our second study we fed diets with a range of NSC contents and showed that under these conditions the threshold for the exaggerated insulin response in ID horses appeared to be between 6-15% NSC on a dry matter basis.
We are currently undertaking a follow-up study, which will hopefully help to identify whether additional starch or sugar is the main driver for the insulin response and further define where the likely NSC threshold range may be when fed such simple diets. Erica Macon explained that ‘when combined with other work showing the potential effects of other nutrients on the insulin response, such as oil inclusion, these results should help with the development of rations that decrease the risk of endocrinopathic laminitis’. As our team is composed of equine enthusiasts, we are dedicated to improving our understanding of this endocrine disorder and the welfare of EMS/ID horses.
This work has been generously funded by Mars Horsecare and The Waltham Petcare Science Institute. Thanks are also owed to Pat Harris, PhD VetMB DipECVCN MRCVS, EBVS® European specialist in veterinary and comparative nutrition and member of European College of Veterinary and Comparative Nutrition, and Amber Krotky MS, PAS and manager of quality and product development at Mars Horsecare US, for their support in completing this project.
By Erica Macon
Erica L. Macon, MS, is a PhD student in the laboratory of Amanda Adams, PhD, MARS EQUESTRIANTM Fellow and associate professor at the Gluck Equine Research Center.
1 Macon, E.L., Harris, P., Bailey, S., Barker, V.D. and Adams, A., 2021. Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared to non‐insulin dysregulated controls. Equine Veterinary Journal online
About the Gluck Center
The mission of the Gluck Center is scientific discovery, education and dissemination of knowledge for the benefit of the health and well-being of horses. Gluck Center faculty conduct equine research in seven targeted areas: genetics and genomics, immunology, infectious diseases, musculoskeletal science, parasitology, pharmacology, therapeutics and toxicology and reproductive health. The Gluck Equine Research Center, a UK Ag Equine Program, is part of the Department of Veterinary Science in the College of Agriculture, Food and Environment at the University of Kentucky.
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