Updated September 2022. 

Research, conducted in collaboration with SPILLERS, shows that even 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 restricting starch and sugar intake maybe beneficial for all senior horses, regardless of whether or not they have PPID or a history of laminitis.

Senior horse

Insulin is a hormone produced by the pancreas. The release of insulin signals cells, especially in the muscle and liver, to take up glucose from the blood. The term insulin dysregulation includes a high basal or 'resting' insulin (in the blood), an exaggerated insulin response to consuming starch and/ or sugar and tissue insulin resistance (failure of cells to respond to insulin).

Two studies, conducted by the Equine Studies Group at the WALTHAM Petcare Science Institute, who provides the science underpinning SPILLERS, in collaboration with Michigan State University, aimed to find out more about the relationship between insulin dysregulation, dietary adaptation, and aging to help guide more appropriate feeding regimens for senior horses.

Both studies investigated tissue insulin resistance and the insulin response in healthy adults compared to healthy senior horses adapted to diets with varying levels and sources of hydrolysable and structural carbohydrate (starch, sugar, and fibre).

Veteran horse grazing

Results from both studies showed insulin responses tend to increase with age in healthy horses, regardless of the diet they had been fed prior to evaluation. The insulin response, for example, was highest in the senior horses fed a starch rich meal even when they had been adapted to such a diet.

These studies confirm that even healthy older horses can have an increased insulin response compared to younger animals. This suggests that the energy sources used in the diet of senior horses and their effect on insulin dynamics needs to be carefully considered. Practically, this means restricting the overall amount of starch and sugar in the diet especially for those horses that already have additional risk factors such as obesity, native breeding or PPID.

These studies are two of a number of our exciting research collaborations aimed at helping to benefit the lives of senior horses in the UK and around the world.

For more advice on feeding your senior horse or pony contact the SPILLERS Care-Line on 01908 226626


  1. Rapson J.L. , Schott II H.C. , Nielsen B.D. , McCutcheon L.J. , Harris P.A. &  Geor J.   Effects of age and diet on glucose and insulin dynamics in the horse. Equine Veterinary Journal https://doi.org/10.1111/evj.12812
  1. Jacob, S. I., Geor, R. J., Weber, P. S. D., Harris, P. A. and McCue, M. E. (2018), Effect of age and dietary carbohydrate profiles on glucose and insulin dynamics in horses. Equine Vet J. 50: 249 - 254. https://doi.org/10.1111/evj.12745