The risk is particularly important during autumn, when acorns fall onto grazing areas. Heavy acorn crops, known as mast years, and strong winds can suddenly increase the number of acorns available to grazing animals.

Are Acorns Poisonous to Horses?

Yes. Acorns can be toxic to horses if consumed in sufficient quantities. Not every horse will eat acorns, but some actively seek them out. The risk may increase when grass availability is poor or large numbers of acorns are present.

Horses can also consume oak leaves, buds and branches, with young leaves and green acorns containing particularly high levels of potentially harmful compounds. 

If a paddock contains oak trees, regular monitoring during autumn is therefore important.

When is The Risk of Acorn Poisoning Highest?

The main risk period is late summer and autumn, when acorns begin to fall.

Risk can increase significantly:

  • During heavy acorn-producing or ‘mast’ years. 2025 was one such year.

  • After strong winds or storms.

  • When grass growth is poor – particularly following summer droughts.

  • Where large numbers of acorns accumulate beneath oak trees.

  • When animals have unrestricted access to affected areas.

Importantly, a paddock that has been grazed safely for years can still become a problem during a particularly heavy acorn fall.

How Can Paddock Managers Prevent Acorn Poisoning?

Prevention is the most effective approach. Paddock managers should consider the following measures.

Identify oak trees

Check paddocks for oak trees and consider trees outside the boundary too. Acorns can fall considerable distances, particularly in windy conditions.

Pay particular attention to areas directly beneath the tree canopy.

Monitor acorn fall

Increase paddock inspections during autumn, particularly following storms and strong winds.

If large quantities of acorns have fallen overnight, reassess whether animals should remain in the field.

Restrict access

Where possible, fence off areas beneath oak trees or move animals to a paddock without acorn contamination.

Temporary electric fencing can be a practical option where permanent fencing isn't suitable.

Remove fallen acorns

On smaller paddocks or concentrated areas, acorns can be collected using rakes, nut gatherers or suitable mechanical equipment.

Removing acorns may reduce the risk, but it can be difficult to clear every acorn from a large or uneven paddock. Where contamination is heavy, restricting animal access is generally the more practical option.

Maintain good forage availability

Keeping grass and forage readily available can reduce the temptation for animals to investigate other food sources.

However, providing hay does not make a heavily contaminated paddock safe. Some animals may continue to eat acorns despite having alternative forage.

Acorn Toxicity: A Simple Paddock Checklist 

During autumn:

  • Monitor the number of fallen acorns.

  • Inspect paddocks after storms and strong winds.

  • Restrict access to heavily affected areas. 

  • Remove acorns where practical.

  • Maintain adequate grass and forage.

  • Watch animals for changes in behaviour, appetite or digestive health.

  • Act quickly if poisoning is suspected.

Protecting Horses from Acorn Toxicity

Oak trees are an important part of the UK landscape and removing them isn't necessarily required. In most situations, careful paddock management can significantly reduce the risk.

The key is to identify potential hazards before animals are exposed to large quantities of acorns. Regular autumn inspections, sensible grazing management and temporary exclusion from heavily affected areas can all help keep horses and livestock safe.

If you need to manage sycamore seedlings, or you are concerned about the quality of your pasture, please get in touch with our technical team today for free, tailored advice.

This post was written in collaboration with Millie Wilkinson. 

Millie Wilkinson

Millie Wilkinson is Agrigem's Account Manager in charge of equine customers. She has more than 12 years' experience in the equine sector including running her own yard, competing for the England team in the Pony Club, working as a showjumping competition groom, and latterly a show-jumping coach. 

Millie has ridden, owned, and sold horses her whole life. She is an established name online where she is an active voice in the latest conversations around elite horses. Millie is a keen proponent of good grazing nutrition and the importance of high-quality paddock maintenance in supporting the health of all horses.