Eventers, show jumpers, endurance horses and racehorses all ask a lot of their digestive systems. To fuel hard work, many receive larger concentrate rations than a leisure horse would, and they often spend more time stabled, travel more and train at higher intensity. Each of those factors can affect the stomach, the hindgut or both. This page explains the main pressures, sets out the ration principles vets and nutritionists work from, and looks honestly at what supplements can and cannot do. It is editorial guidance from Horse Probiotics, and your vet and nutritionist should shape the plan for your own horse.
Why hard work challenges the gut
More starch
Cereal-based feeds supply energy in concentrated form, but starch is best digested in the small intestine and there is a limit to how much a large meal allows. Starch that escapes into the hindgut is fermented quickly. In a study published in the Journal of Animal Science, horses moved abruptly onto a higher-starch ration had lower caecal pH over the following week and shifts in their caecal bacteria compared with horses on a lower-starch ration.
The stomach under pressure
The European College of Equine Internal Medicine (ECEIM) consensus statement on gastric ulcers in adult horses, published in the Journal of Veterinary Internal Medicine, describes several risk factors for squamous gastric disease that apply to performance horses. The prevalence and severity of lesions rise with the intensity of training. Starch intake above 2 g per kg of bodyweight per day was associated with roughly double the likelihood of more significant squamous disease. Gaps of more than six hours between forage meals, straw as the only forage, and lack of constant access to water were also linked to higher risk.
Lifestyle
Many performance horses have restricted turnout to protect them from injury, travel frequently and live to a timetable set by training and competition. Less grazing time means longer gaps between forage intake, and frequent changes of stabling add the kind of disruption covered on our travel and competition page.
Ration design comes first
The principles below come largely from the ECEIM statement and are widely used as a starting point. They are not a substitute for a ration designed for your individual horse.
- Forage as the foundation. The statement suggests that horses fed hay receive a minimum of 1.5 kg of dry matter per 100 kg of bodyweight per day, with free-choice hay or at least four to six forage meals a day.
- Limit starch. It recommends no more than 2 g of starch per kg of bodyweight per day and no more than 1 g per kg per meal. For a 500 kg horse that means a ceiling of around 1 kg of starch a day and 500 g in any one feed. A feed with 25% starch would reach the per-meal limit at 2 kg, so check the starch figure on the bag or ask the manufacturer.
- Space hard feeds. The statement suggests concentrate meals are fed at least six hours apart.
- Use fibre and oil for energy. Digestible fibres and oil can provide calories with less reliance on cereal starch.
- Do not rely on straw alone. Straw can form part of the forage, but the statement advises against it being the only forage provided.
- Water at all times, at home, in the lorry and at the venue.
A balanced ration also needs the right vitamins and minerals. If your horse is fed less than the recommended amount of a compound feed, the gap is usually filled with a balancer or a vitamin and mineral supplement, and our comparison of a feed balancer and a vitamin and mineral supplement explains the choice.
Where supplements may or may not help
Live yeast and prebiotics
Performance horses are the group where the case for live yeast is most plausible. A 2022 review in Animals found that effects on lactate-producing and lactate-using bacteria were more consistent in horses on high-concentrate diets, and one study it describes reported higher caecal pH and lower lactate with yeast on that type of diet. The same review describes the overall body of evidence as contradictory and highly variable, so a yeast product should be seen as a possible support for a well-designed ration rather than a way to feed more starch safely. Our equine probiotics guide explains strains and inclusion levels.
Horse Probiotics does not make performance claims for any product, and you should be wary of any that do. A gut supplement is designed to support normal digestion, which is one part of keeping a working horse comfortable and in condition.
Gastric support
Products for the stomach and products for the hindgut do different jobs. The ECEIM statement is clear that gastroscopy is the only reliable way to determine whether a living horse has gastric ulcers, so a horse with suspected ulcers needs a diagnosis before anyone decides on treatment or supplementation. Our gastric supplements guide and the gut balancer vs gastric supplement comparison explain the difference.
Electrolytes
Horses in hard work lose electrolytes in sweat. The ECEIM statement considered electrolytes mixed into feed to be safe but linked oral electrolyte pastes and hypertonic solutions to increased risk of squamous gastric disease. Our electrolytes guide covers when and how to use them.
Label quality
Quality varies between products. A review in the Journal of Veterinary Internal Medicine reported that only 2 of 13 veterinary and human probiotic products tested contained the labelled organism at the stated concentration. Choose products that name the strain and state the amount, and compare them in the reviews hub.
Competition rules
For competing horses, every feed and supplement should be checked against the rules of the relevant governing body. BETA's NOPS scheme is designed to reduce the risk of naturally occurring prohibited substances in feed, and BETA notes that the British Equestrian Federation requires squad members to use only NOPS accredited products. Use BETA's webchecker to confirm a company's membership.
Signs to watch
In horses in hard work, digestive discomfort often shows up first as a change in performance or attitude rather than an obvious physical sign.
- Loss of condition despite a high-energy ration
- Girthiness, resistance or reluctance to go forward
- Leaving feed or eating more slowly
- Loose droppings after travel or competition
- A drop in performance without an obvious musculoskeletal cause