Live long and prosper: How science is helping senior horses

Some of the latest collaborative work by Spillers includes a potentially ground-breaking study to improve the understanding of Pars Pituitary Intermedia Dysfunction (PPID).
Some of the latest collaborative work by Spillers includes a potentially ground-breaking study to improve the understanding of Pars Pituitary Intermedia Dysfunction (PPID). © Claire Dyett / Spillers

A collection of research on the nutrition of senior horses, with a particular focus on Pars Pituitary Intermedia Dysfunction (PPID), is being made available by feed manufacturer Spillers.

The company, via the Waltham Equine Studies Group, is involved with numerous research collaborations which bring together world-leading equine veterinary, nutrition and research experts to support the wellbeing, performance and longevity of senior horses and ponies.

It also has a new collaborative research project in the pipeline to help improve the understanding and knowledge of the causes of PPID ( formerly termed Equine Cushing’s Disease) as well as early diagnosis, treatment, husbandry and nutritional management.

Spillers Product Manager Sarah Nelson says the company has been involved in senior horse research for more than 20 years.

“Here at Spillers senior horses hold a special place in our hearts. By translating our science and sharing highlights and practical take-home messages we hope to give the owners of seniors the extra support they need to help keep their horses in the best possible health.”

Spillers Equine Clinical Nutrition Specialist Pat Harris is continuing to share the latest work on senior nutrition by giving talks and delivering practical courses to vets around the world. Harris is also co-author of a paper to be published shortly in Equine Veterinary Education on nutritional considerations for the management of equine PPID.

The findings from several other collaborative research projects will soon be shared, including the investigation of the primary use and current exercise regimen of US senior horses; risk factors and reasons for retirement; prevalence, risk factors for and consequence of low muscle mass in this population; and development and evaluation of a muscle atrophy scoring system (MASS) for horses.

Although the reasons are not yet clear, research findings may suggest that ponies ‘age later’ than horses.
Although the reasons are not yet clear, research findings may suggest that ponies ‘age later’ than horses. Photo: Spillers

Previously published research includes:

Short journeys may cause stress in seniors

It’s well known that long-distance transport increases stress and compromises immune function, but what about the effects of shorter journeys on seniors, given that we know ageing can lead to low-grade inflammation? A recent study in senior horses found that travelling for 1.5 to 2 hours in a trailer increased certain markers of stress and inflammation. More work is already under way to help better understand the practical implications of this.

Hay only diet not good enough

A Spillers study published in 2014 found that in healthy horses, ‘being senior’ did not affect energy, protein or NDF (fibre) digestibility regardless of the type of diet fed (hay only, hay plus a starch and sugar-based feed or hay plus a fibre and oil-based feed). Similar findings were found in another of our studies with ponies.  A follow-up study also showed there was also no effect of age on mineral digestibility in horses.

Older horses may be more sensitive to changes in diet

The horse’s hindgut is home to trillions of tiny microbes including bacteria, viruses and fungi which are essential for fibre digestion and helping to regulate the immune system. Research in healthy horses found that ageing led to a reduction in the diversity of hindgut microbes, which may make some older horses more sensitive to changes in diet. Interestingly, no reduction in diversity was seen when this research was repeated in similarly aged ponies. Although the reasons for this are not yet clear, these findings may suggest that ponies ‘age later’ than horses.

Restricting starch and sugar may be beneficial to seniors

Insulin dysregulation (which includes a high basal insulin, and/or an exaggerated insulin response to consuming starch and/or sugar and tissue insulin resistance) can be present in some horses with PPID and is associated with an increased risk of laminitis. However, two studies that investigated the relationship between age, diet and insulin dysregulation found that even healthy senior horses typically have an increased insulin response to a meal high in starch and/or sugar. This suggests that restricting starch and sugar intake may be beneficial for all senior horses, regardless of whether or not they have PPID or a history of laminitis.

Spillers is working to refine guidance on the level of starch and sugar to be fed to older equines with insulin dysregulation and a study on this topic is to be published in the Equine Veterinary Journal shortly.

High starch diet could potentially lead to a false PPID diagnosis

Diagnosis of PPID involves a blood test that measures the level of adrenocorticotropic hormone or ‘ACTH’ in the blood. Diagnosis can be notoriously difficult because ACTH levels can be affected by several factors including the time of year and even ageing itself. However, research has shown that a high starch diet can also increase the concentration of ACTH in the blood which could potentially lead to a misdiagnosis of PPID.



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. and 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), p.e87424

Elzinga, S., Nielsen, B.D., Schott II, 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), pp. 1164-1169.

Elzinga S., Nielsen BD., Schott HC., Prapson J., Robison CI., McCutcheon J., Geor R.J., Harris P.A. (2017) Comparison of nutrient digestibility between three diets for aged and adult horses DOI: Journal of Equine Veterinary Science, Vol. 52, p89

Galinelli N., Bailey S., Bamford N., Harris P.  Nutritional considerations for the management of equine pituitary pars intermedia dysfunction Equine Veterinary Education in press

Herbst, A.C., Johnson, M.G., Gammons, H., Reedy, S.E., Urschel, K.L., Harris, P.A. and Adams, A.A., (2021). Development and evaluation of a muscle atrophy scoring system (MASS) for horses. Journal of Equine Veterinary Science, p.103771

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 Vet J. 50: 249 – 254.

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 adrenocorticotropic hormone (ACTH) and cortisol concentrations in adult and aged horses. Domestic Animal Endocrinology, 63, 15-22

Macon, E.L., Harris, P., Bailey, S., Barker, V.D., Adams, A., (2021). Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared to non‐insulin dysregulated controls. Equine Veterinary Journal in press

Miller AB, Harris PA, Barker VD, Adams AA (2021) Short-term transport stress and supplementation alter immune function in aged horses. PLoS ONE 16(8): e0254139. https://doi. org/10.1371/journal.pone.0254139

Morrison PK, Newbold CJ, Jones E, Worgan HJ, Grove-White DH, H. Dugdale AH, Barfoot C, Harris PA & Argo CM (2018) The equine gastrointestinal microbiome: Impacts of age and obesity. Front. Microbiol., 07 December 2018

Rapson J.L., Schott II H.C., Nielsen B.D., McCutcheon L.J., Harris P.A. and Geor J. (2018) Effects of age and diet on glucose and insulin dynamics in the horse. Equine Veterinary Journal

Latest research and information from the horse world.

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