During competition, most endurance horses cannot eat nor digest sufficient feed at each veterinary check to produce the ATP required to meet the energy requirements for the next leg/loop. It is essential therefore that you fill up the fuel tank (energy reserves) before the event. A 400kg horse can store approximately only 13,000 cal/kg as glycogen, but a massive 590,000 cal/kg as fat! That is the good news. The bad news is that horses can only use these fat reserves if they are metabolically adapted, fed the right oils, and not overloaded with high Non Structural Carbohydrate (NSC or grain) feeds.
Feeding Oils. There is good logic as to why you should feed oils to an endurance horse. Oils contain 2.5 times more energy than carbohydrate. It produces 3 times more ATP than carbohydrate under aerobic conditions, and horses can store 40 times more energy as fat. It is imperative, however, that the diet remains balanced for carbohydrate, protein, fibre, minerals and vitamins, since overfeeding oils can cause reduced fibre digestion and unbalanced mineral supply. The constraint to efficient fat utilisation however is that the energy (ATP) from fat can only be released when carbohydrate (grain) intake is low, ie. When INSULIN levels are low. Also, it takes 2-3 weeks for a horse to become fat adapted, i.e. for the metabolic pathways, hormones and enzymes to switch to using oil rather than carbohydrates and glycogen.
This removes the need to feed expensive Omega 3 oils. If horses are grazing pasture, and well prepared hays, they will usually eat enough Omega 3 to meet dietary requirements. (Refer to the great book Equine Applied and Clinical Nutrition, expensive but worth it for all horse owners). Which oil? The key is to select a balance of oils that are palatable, haven’t been highly processed, do not go rancid, provide the correct balance Omega 6:3:9 and that deliver ATP to meet the horses energy demands under aerobic conditions. Most oils are absorbed and transported slowly to the liver via the lymphatics. The medium chain triglyceride (MCT) oils such as coconut oil however are unique in that they are absorbed directly into the portal blood and transported directly to the liver. Coconut oil therefore is used as a non-glucose source of ready energy. One of the main advantages of coconut oil is that when compared to PUFA oils, it improves muscle glycogen storage and utilisation. Most importantly, feeding oils also reduces thermal load, which is critical for recovery under heavy work load and hot conditions.
Why feeding twice a day can be bad. We usually feed our horses twice daily because it suits our busy lifestyle. If we feed high NSC feeds, this creates spikes in both insulin and glucose, which cause hormonal shifts that switch off fat adaptation and fat utilisation pathways. In a published nutritional study of horses at pasture, when given feeds of different NSC content, the sweetfeed (33% NSC) and pelleted (25% NSC) feeds gave large spikes in both insulin and glucose. By comparison, 2.3kg/day of copra meal (10% oil, 11% NSC, 15 MJ digestible energy) did not metabolically increase glucose or insulin (Richards et al 2016 Animal Feed Science and Technology). Copra meal is the only high energy, low NSC feed that can be fed to endurance horses as single feed that does not have a negative influence on insulin and glucose levels.
The next article will discuss how to adapt your horse to a high fat diet, and what other supplements are required to optimise aerobic performance and fat utilisation.