Should I Give My Horse Probiotics?

By Dr Duncan Houston

A healthy horse does not automatically need a daily probiotic. There may be situations where a particular product is worth considering, but the reason for using it should be clear.

For a horse with loose manure, poor appetite or colic, the first step is to assess what is causing the change. Adding a digestive supplement should not delay that assessment.

Quick answer

Probiotics may be useful for selected horses as part of a veterinary or nutritional plan, but evidence varies between products and conditions. A healthy adult horse with a suitable diet and normal manure does not necessarily benefit from routine supplementation. Foals need particular caution, and watery diarrhoea or signs of colic warrant an immediate call to your vet, rather than a trial of probiotics.

Why gut microbes matter so much to horses

Horses are hindgut fermenters. Microorganisms in the caecum and large colon break down fibre from forage, producing compounds the horse can use for energy.

This makes the diet and the microbial community closely connected. Feeding practices that disrupt fermentation can contribute to digestive problems. A supplement cannot compensate for unsuitable feeding management.

Probiotics contain live microorganisms intended to provide a health benefit. Equine products may contain bacteria, live yeast or a combination. Prebiotics are different: they are ingredients intended to support beneficial microbial activity.

What does the evidence show?

There is a plausible reason to support the equine microbiome, but clinical evidence for many commercial probiotic products remains limited. Research also raises questions about whether some products contain the organisms and amounts claimed on their labels.

Live yeast, such as particular strains of Saccharomyces cerevisiae, has been studied for its effects on digestion. Some trials have reported improvements in nutrient or fibre digestibility, while others found no meaningful improvement. Results depend on the strain, diet and study conditions.

Improved digestibility in a feeding trial does not prove that a product treats diarrhoea or prevents colic. The benefit you want should match the outcome actually studied.

When might a probiotic be considered?

Your vet or equine nutritionist might consider a specific product:

• As an optional addition to a feeding plan with a defined nutritional goal.

• During recovery from a diagnosed digestive problem.

• Around medication or management changes, after reviewing the individual horse’s risks.

These are reasons to discuss a product, not guarantees that supplementation will help. Ask what improvement is expected and how you will decide whether it is worth continuing.

Be especially cautious with foals

Foals have a developing intestinal microbial community. Findings from adult horses cannot simply be applied to them.

Some controlled foal studies found no preventive benefit from the probiotic tested and reported potential adverse effects, including more serious diarrhoea requiring veterinary attention.

Do not routinely give a newborn foal probiotics unless your vet recommends the specific product. A foal with diarrhoea needs prompt veterinary advice, particularly if they are dull, weak or nursing less.

How urgent is the situation?

Your horse’s condition	What to do
Healthy adult, normal appetite, weight and manure	Review the diet before adding an optional supplement.
Slightly softer manure, but otherwise bright and comfortable	Monitor closely and discuss persistent or recurring changes with your vet.
Watery diarrhoea, fever, reduced appetite or marked dullness	Call your vet immediately for assessment and instructions.
Pawing, flank-watching, repeated rolling, sweating or reduced manure with discomfort	Treat as possible colic and call immediately.
Foal with diarrhoea, especially with weakness or reduced nursing	Contact your vet promptly. Do not start with a supplement trial.

The horse’s behaviour, appetite and hydration are more useful for judging urgency than whether a probiotic is available in the feed room.

What else could be causing loose manure?

Possible causes include changes in feed, intestinal parasites, infectious disease, sand accumulation, inflammatory disease and medication-related intestinal injury.

Recent antibiotics, anti-inflammatory medication, travel, feed changes and illness in other horses are all relevant details for your vet. Depending on the examination, they may recommend manure testing, blood tests or further investigation.

A diagnosis of “gut imbalance” should not become a reason to overlook these possibilities.

When is this an emergency?

Call your vet immediately for colic signs, profuse watery diarrhoea, severe weakness, collapse or rapidly worsening illness.

If colic is suspected, remove access to feed while you seek veterinary instructions. Keep water available unless your vet advises otherwise. Do not force oral supplements, fluids or medication into a distressed horse. Keep yourself safe around a horse that is rolling or thrashing.

Separate a horse with acute diarrhoea from other horses while seeking advice. Use dedicated buckets and equipment, wash your hands and follow your vet’s biosecurity instructions. Some causes can spread between horses or infect people. Tell the clinic about the diarrhoea before travelling there.

How to choose and use a probiotic sensibly

1. Define the goal

Be specific about what you are trying to improve. Is your horse recovering from a diagnosed illness, or has a nutritionist identified a reason to trial a particular live yeast?

If your horse is healthy and there is no clear goal, a supplement may add cost without a measurable benefit.

2. Check the product

Look for clear information about:

• The exact microorganisms and strains.

• Research in horses of the relevant age and with the relevant problem.

• The amount of viable organisms provided.

• The expiry date, storage requirements and recommended dose.

• Quality-control information from the manufacturer.

A higher colony-forming unit count, often written as CFU, does not automatically mean better results.

3. Follow the agreed plan

Use the recommended dose and storage conditions. Avoid adding several digestive supplements at once, and tell your vet about medications already being given.

Record appetite, manure consistency, manure frequency and any signs of discomfort. Agree on a review point rather than continuing indefinitely without knowing whether the product helps.

If your horse deteriorates, contact your vet. Increasing the probiotic dose is not an appropriate response to worsening illness.

What matters most for everyday gut health?

Start with the feeding and management basics:

• Provide suitable, good-quality forage within a balanced feeding plan.

• Make changes to hay, pasture and concentrates gradually.

• Avoid unnecessarily large concentrate meals.

• Maintain access to clean water and check actual intake.

• Keep dental care and veterinary parasite management up to date.

• Provide appropriate movement, turnout and a predictable routine.

Horses with metabolic disease, dental problems or other medical needs require an individual plan. A probiotic should fit within that plan.

Common mistakes to avoid

• Assuming a product studied in dogs or people will work in horses.

• Treating all yeast products as equivalent to a studied live-yeast preparation.

• Giving probiotics routinely to foals without veterinary advice.

• Using supplements to compensate for abrupt feed changes.

• Waiting for a supplement to work while a horse has diarrhoea or colic.

Frequently asked questions

Should a healthy horse have probiotics every day?

Not automatically. Routine use needs a clear purpose and evidence relevant to the product. Review forage, water, feeding consistency and general health before adding another daily supplement.

Should I give probiotics after antibiotics?

Discuss it with the prescribing vet. Antibiotics can disturb the intestinal microbiome, but probiotics are not a guaranteed way to prevent or reverse that disturbance. Diarrhoea during or after antibiotic treatment warrants an immediate call to your vet.

Can I give my horse a human or dog probiotic?

Do not assume it is suitable. The strains, formulation and supporting research may not apply to horses. Ask your vet to assess the specific product rather than estimating a dose from body weight alone.

Will probiotics stop colic?

They are not a treatment for an active colic episode. Colic can involve obstruction, displacement, inflammation or other serious disease, and the correct treatment depends on the cause. Call your vet when signs appear.

ASK A VET™ supports informed decisions about animal health and care. For your horse, start with a clear reason for supplementation, a suitable feeding plan and veterinary assessment whenever their appetite, manure or behaviour changes.