When fresh grass suddenly takes off, your horse’s diet can change remarkably quickly, even though they haven’t changed paddocks.

For some horses, one of the first things owners notice is softer, poorly formed or watery manure. While diarrhoea can have many causes, if it coincides with a sudden increase in fresh pasture, the speed of that dietary change is worth considering.

The microbial population of the hindgut adapts to what your horse eats. When the diet changes, those microbes need time to adjust.

Introduce pasture gradually and give the gut time to catch up with the grass.

At a Glance

If your horse develops loose manure as the grass changes:

• Consider how quickly their pasture intake has increased

• Avoid suddenly going from predominantly hay to large amounts of fresh grass

• Introduce new pasture gradually where possible

• Keep adequate forage and fibre in the diet during the transition

• Avoid making several major feed changes at once

• Monitor manure, appetite, water intake and general demeanour

• Seek veterinary advice for significant or persistent diarrhoea, or if your horse appears unwell

Why Can Spring Grass Cause Problems?

Spring can bring a surprisingly dramatic change in diet. A paddock that provided very little feed through winter can suddenly produce large amounts of young, actively growing grass. Fresh pasture differs from mature hay in its moisture, nutrient and carbohydrate profile, and horses may also substantially increase the amount they consume.

The horse’s hindgut contains a complex community of microorganisms responsible for fermenting fibre and helping the horse extract nutrients from forage. These microbial populations respond to changes in the diet, but adaptation takes time.

Research presented at the 2025 No Laminitis! Conference followed horses transitioning between different pasture types and demonstrated that their hindgut microbial populations adapted during the transition. This supports a simple principle that has long been important in horse feeding: make dietary changes gradually.

What Can You Do?

If your horse has been eating hay predominantly and the paddocks suddenly begin growing, try to avoid going from very little grass to unrestricted access overnight. 

Increase pasture access gradually where practical, continue providing appropriate forage, and avoid changing several other parts of the diet at the same time.

Manure is also a useful daily indicator. If it becomes consistently softer as pasture intake increases, consider whether the dietary transition is happening too quickly.

Can Gut Support Help?

Digestive supplements can provide additional support during periods of dietary change, but they don’t replace good feeding management.

Missy’s Bucket Gut-Plus contains Yea-Sacc and Bio-Mos, two yeast-derived technologies developed by Alltech. 

Yea-Sacc is a specific Saccharomyces cerevisiae yeast culture that has been researched in horses for its effects on hindgut fermentation, fibre digestion and microbial populations. 

Bio-Mos is a yeast-derived product used to support gut health, gut integrity and the animal’s natural defences.

These can be useful tools when the diet is changing, but the foundation remains the same: you cannot supplement your way out of an abrupt dietary change.

When Is Diarrhoea More Than “Spring Scours”?

Not every case of loose manure is caused by grass. Diarrhoea can have many causes, including potentially serious gastrointestinal disease.

If diarrhoea is profuse or persistent, or your horse has a fever, colic signs, reduced appetite, lethargy, dehydration or simply appears unwell, contact your veterinarian.

The Bottom Line

Spring grass doesn’t just mean the paddock is changing. Your horse’s diet is changing too.

Introduce pasture gradually, maintain adequate forage, watch the manure and give the hindgut time to adapt. Digestive support can help support that transition, but good management comes first.

Give the gut time to catch up with the grass.

Primary Resources:

• Gustafson KM. Factors Affecting Forage Carbohydrates. ECIR Group, 2025 No Laminitis! Conference.


• 2025 No Laminitis! Conference proceedings, research on microbial adaptation during pasture transitions.


• Alltech equine technical information and research bibliography for Yea-Sacc and Bio-Mos.