Q: I have a mare with PPID and I was going to feed vegetable oil as a safe way to put weight on her, but I have concerns since I’ve read that feeding oil can increase glucose intolerance and insulin resistance. Can I add oil to her feed?

A: Vegetable oil is a safer way to cause weight gain than starchy or sugary feeds for most horses and ponies. However, as with all feeds and supplements, the whole case must be looked at before deciding what is best.

Not all horses with PPID have glucose and insulin disturbances, and it should not be confused with equine metabolic syndrome (EMS). The condition known as equine metabolic syndrome (EMS) includes obesity, insulin resistance and laminitis (it’s not a disease as such, but a definition of a collection of symptoms) – therefore supplementary oil at any more than a very small amount should be avoided because it may worsen the insulin resistance and it will add unwanted calories (dietary energy) for an animal who needs to lose body fat.


We know that high fat diets worsen insulin resistance in most species and work by Pagan and others at Kentucky Equine Research showed that high fat diets worsened impaired glucose tolerance in aged horses. Oil is more calorific per gram than carbohydrates so should be kept to a minimum for overweight horses and ponies that need to lose body fat.

Although PPID can involve glucose and insulin disturbances, if it is managed correctly, the relevant medication given and the horse kept at a healthy weight, then the horse’s metabolism should be stablised and they should be able to cope with a controlled amount of supplementary oil in their diets, if they are lacking condition and the diet has already been adjusted accordingly. These horses should be monitored regularly by the vet. The amount of oil to feed would be a maximum of 200 ml for a typical 500 kg horse, split into at least 2 feeds per day. They would not normally be fed a high fat diet as defined by what would be fed to a hard working performance horse. Useful oils include cold-pressed linseed (flaxseed) and cold-pressed rapeseed.

PPID affected horses and ponies should always be fed plenty of good quality protein, which is important for them to maintain good condition. They should also be fed vitamins and minerals to balance forage (either in a feed, balancer or supplement), and extra antioxidant vitamins E and C (especially if supplemented with oil).

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About Clare MacLeod

Clare MacLeod MSc RNutr is one of the UK’s few registered independent equine nutritionists who also has expertise in health and fitness. She advises private and commercial clients in all sectors of the horse world and is a hands-on horse owner herself. Clare is passionate about correct nutrition as a foundation for good health, without which peak fitness is not possible. She states “Good nutrition isn’t everything, but there’s nothing without it”.