Research overview: Preventing laminitis by studying insulin dynamics in older horses

Laminitis research comes in many forms. Recently, the emphasis has been on understanding the cause of the disease, and developing ways to prevent horses from ever knowing laminitic pain. The emphasis is on understanding how horse management and feeding can effect hormonal balances in older horses, and what recommendations might help horses live longer and healthier lives.

As the proportion of aged horses within the general equine population appears to be increasing in many countries, the WALTHAM® Equine Studies Group of researchers fine-tuned their efforts even more, through an international effort at multiple universities on three continents to add to the body of knowledge in identifying and managing insulin dysregulation, and providing the optimal care and feeding of older horses. Insulin has been identified as a critical hormone with a role in laminitis.

At the Australasian Equine Science Society’s Science Symposium earlier this month, Professor Pat Harris, head of the WALTHAM® Equine Studies Group, summarized her group's research on the care of senior horses. In Great Britain, Waltham's products are sold under the "SPILLERS®" brand.

WALTHAM’s journey into the feeding and management of the senior horse started in earnest at England's Nottingham Trent University in the early 2000s, with funding of a PhD program investigating age-related changes in taste and feeding behavior in the stabled horse. Studies continued at Michigan State University, looking at the effect of age on digestive function followed by the effect of diet on glucose and insulin dynamics.

Collaborative work is currently ongoing at the University of Minnesota, Michigan State University, the University of Kentucky and Australia's University of Melbourne on the role of diet on tissue insulin resistance and the insulin response to an oral starch or sugar-rich meal, as well as the gut microflora in the older horse.

The SPILLERS® team in the United Kingdom has also been working with colleagues at the universities of Aberystwyth, Surrey and Liverpool, studying the microflora of the older horse or pony and its response to dietary changes.

In conjunction with the University of Kentucky, SPILLERS® has been looking at the relationship between nutrition and the chronic inflammation associated with aging and Pituitary Pars Intermedia Dysfunction (PPID, or Equine Cushing's Disease); and with respect to PPID specifically, work at Michigan State and the Royal Veterinary College (RVC) in London has looked at the effect of diet and analytical method on Adrenocorticotropic hormone (ACTH) concentrations respectively. 

Some of the research findings to date include:

• The horse’s ability to digest key nutrients does not appear to decrease with age in studies of healthy adult and aged horses of similar type although some differences in the microflora in the gut may be present. This is now being studied further in the pony. (See references 1, 2, 3 below)
• Healthy older horses have increased insulin responses, compared to younger horses, in response to a starch-rich or starch- and sugar-rich meal. This suggests that older horses, whether or not they have been diagnosed with insulin dysregulation, need an appropriate diet and management plan to help minimize the risks associated with insulin dysregulation such as laminitis.
  In practical terms, this means restricting the overall amount of starch and sugar in the diet especially for those horses/ponies that already have additional risk factors such as obesity, native breeding or PPID. (See references 4 and 5 below.)
• Diet can influence adrenocorticotropic hormone (ACTH) concentrations, which are measured to test for PPID, as can the method of analysis of ACTH.  (See references 6 and 7 below.)

Professor Harris said: “Our collaborations bring together world-leading equine veterinary, nutrition, and research experts interested in working on the important topic of the older horse. We are committed to continuing to undertake work that helps support the wellbeing, performance and longevity of senior horses.”

The research group provided a list of recent papers detailing their accomplishments in equine research for the benefit of older horses. Click the linked article titles to read the abstract of each study on the journal's site. Readers with university or other library access can proceed further and download the full article; others may opt to pay for download privileges or seek the article through a reference librarian or alternative resource. 

Note: Article #3 is published in an Open Access journal and may be downloaded by anyone.

1. Elzinga, S., Nielsen, B. D., Schott, H. C., Rapson, J., Robison, C. I., McCutcheon, J., Harris, P.A. & Geor, R. (2014). Comparison of nutrient digestibility between adult and aged horses. Journal of Equine Veterinary Science, 34(10), 1164-1169. 

2. Elzinga, S., Nielsen, B. D., Schott, H. C., Rapson, J., Robison, C. I., McCutcheon, J., Geor, R. and Miller, P. A. (2017). Comparison of nutrient digestibility between three diets for aged and adult horses. Journal of Equine Veterinary Science, 52, 89. 

3. Dougal, K., de la Fuente, G., Harris, P. A., Girdwood, S. E., Pinloche, E., Geor, R. J., Nielsen, B.D., Schott II, H.C., Elzinga, S. & Newbold, C. J. (2014). Characterisation of the faecal bacterial community in adult and elderly horses fed a high fibre, high oil or high starch diet using 454 pyrosequencing. PloS one, 9(2), e87424. 

4. Rapson, J. L., Schott, H. C., Nielsen, B. D., McCutcheon, L. J., Harris, P. A., & Geor, R. J. (2015). Effects of age and diet on glucose and insulin dynamics in the horse. Equine Veterinary Journal. 

5. Jacob, S. I., Geor, R. J., Weber, P. S. D., Harris, P. A., & McCue, M. E. (2018). Effect of age and dietary carbohydrate profiles on glucose and insulin dynamics in horses. Equine veterinary journal, 50(2), 249-254. 

6. Jacob, S. I., Geor, R. J., Weber, P. S. D., Harris, P. A., & McCue, M. E. (2018). Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses. Domestic animal endocrinology, 63, 15-22. 

7. Knowles, E. J., Moreton‐Clack, M. C., Shaw, S., Harris, P. A., Elliott, J., & Menzies‐Gow, N. J. (2017). Plasma adrenocorticotropic hormone (ACTH) concentrations in ponies measured by two different assays suggests seasonal cross reactivity or interference. Equine veterinary journal.

All of the peer-reviewed articles listed in this Hoof Blog post have previously been indexed in monthly editions of HoofSearch, a summary report on equine research related to hoof science, laminitis, and equine lameness. Click here to learn more about HoofSearch.  Or, click here to order your monthly subscription.

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