9 min read Last updated: January 2026 Oak trees in your paddocks feel harmlessuntil acorns start dropping and your horses health is on the line. This guide shows you exactly when risk spikes (SeptemberNovember and spring), the urgent signs to spot, and simple preventionlike a 5-minute daily field scan and fencing to the driplinefor safer turnout. Quick Summary Short on time? Here are the key takeaways. Area: Peak Risk Windows What To Do: Mark SeptemberNovember and the spring flush on your yard calendar; increase checks and restrict access during these periods, especially after heat or storms. Why It Matters: These windows bring the highest acorn drop and tender oak growth, raising poisoning risk. Common Mistake: Assuming fields are safe after winter and overlooking the spring bud risk. Area: Daily Field Checks What To Do: Spend five minutes before turnout scanning under canopies; remove clusters of green acorns and fallen branches and adjust turnout if heavy fall is noted. Why It Matters: Quick, routine sweeps prevent ingestion before it happens. Common Mistake: Turning out first and planning to clear later. Area: Fence Off Oaks What To Do: Put temporary electric fencing to at least the dripline and check after storms; place water and hay 3050 metres away to anchor horses in safer zones. Why It Matters: Physical exclusion stops even determined acornseekers. Common Mistake: Fencing only the trunk and leaving the fall zone accessible. Area: Provide Ample Forage What To Do: Offer adlib hay/haylage in safe areas and rotate fields to avoid overgrazing; move feeding stations well away from oak lines. Why It Matters: Wellfed horses are less likely to browse toxic material. Common Mistake: Relying on sparse grazing during dry spells. Area: Spot Early Signs What To Do: Monitor daily for inappetence, colic, constipation turning to diarrhoea, mouth ulcers, altered urination, or dark urine; note changes and times. Why It Matters: Fast recognition enables earlier veterinary care and a better prognosis. Common Mistake: Waiting to see if it passes before phoning the vet. Area: Suspected Poisoning Steps What To Do: Call your vet immediately; remove the horse from pasture, provide fresh water and forage, and gather sample acorns/leaves plus photos. Why It Matters: There is no antidote and timely supportive treatment can be lifesaving. Common Mistake: Giving activated charcoal or other remedies without veterinary direction. Area: Clear Falls Fast What To Do: Rake or sweep highdensity zones daily in peak season; use a paddock sweeper for larger areas and prioritise green acorns and young leaves. Why It Matters: Rapid clearance reduces exposure where horses graze most. Common Mistake: Delaying cleanups after windy nights or storms. Area: Feed & Treat Safety What To Do: Buy reputable, labelled feeds; avoid any product listing oak parts or unapproved botanicals and contact manufacturers about unclear ingredients. Why It Matters: Oak derivatives arent authorised and tannins are harmful even in small amounts. Common Mistake: Assuming natural ingredients are automatically safe for horses. In This Guide What is oak and acorn poisoning in horses? When are UK horses most at risk? How much is dangerous, and what signs should you watch for? What should you do immediately if you suspect acorn poisoning? How can you prevent acorn access in UK paddocks? Are oak derivatives allowed in UK horse feeds and treats? What seasonal yard management helps reduce acorn risk? Oak trees are a fixture of British fields, but their leaves and acorns can put horses at real risk each spring and autumn. Knowing when danger peaks, what to look for, and how to prevent access could save your horses life.Key takeaway: All parts of the oak are toxic to horses, with young leaves and green acorns the most harmful; poisoning is rare but lifethreatening, so fence off oaks, supply ample forage, and call your vet immediately if you spot symptoms.What is oak and acorn poisoning in horses?Oak and acorn poisoning occurs when a horse eats enough oak material (leaves, buds, bark, acorns) containing tannic acids to damage the gut, kidneys, liver, and blood cells. All parts of the oak are toxic, but new buds, young leaves, and green (juvenile) acorns are the most dangerous.Tannins (tannic and gallic acids) irritate and inflame the digestive tract and can lead to kidney and liver damage. While many horses dislike the bitter taste and avoid acorns, poisoning does happenparticularly where grazing is poor or some horses develop a taste for acorns and seek them out despite plenty of forage.If eaten, acorns, leaves and branches from oak trees pose a risk of poisoning to horses... Acorns contain a substance called tannic acid, which when eaten in sufficient quantity... the tannins can cause serious illness. British Horse SocietySignificant ingestion is generally required for toxicity, but once clinical signs begin, the condition is a veterinary emergency with a high mortality rate and a prolonged recovery (two months or more) for survivors.When are UK horses most at risk?Risk peaks in autumn (SeptemberNovember) during the acorn fall and again in spring with the emergence of new buds and young leaves, especially after hot, dry summers or following storms that bring down extra acorns and branches.UK fields often face grazing shortages after long, dry summers, making acorns a tempting alternative. Overgrazed paddockscommon on busier livery yardscompound the risk. After autumn storms or strong winds, more acorns and branches drop; check fields thoroughly before turnout. Some horses learn to relish acorns and will forage for them even when hay or haylage is provided, so physical exclusion with fencing is crucial.In most cases, paddocks become safe again by late winter once trees have finished dropping and seasonal leaf fall has decomposed or been cleared. However, the spring flush of tender oak growth creates a second, often-overlooked risk window when other grazing is still limited.How much is dangerous, and what signs should you watch for?Toxicity typically requires eating large quantities of acorns or oak leaves, but if symptoms appear, it is always an emergency with a guarded prognosis. Early recognition and immediate veterinary care are critical.Because intake varies by tree, season, and individual horse, theres no single safe number of acorns. Instead, focus on prevention and vigilance. Watch closely from early autumn through late autumn (and again in spring) for:Reduced appetite, dullness, or depressionConstipation or colic that may progress to diarrhoeaDehydration and increased drinking/urination or, conversely, reduced urinationMouth ulcers or droolingDark or bloody urine (a sign of red blood cell damage)Abdominal pain, tucked-up appearance, or strainingHorses must consume a large amount of oak leaves or acorns to cause toxicosis, however the mortality rate is high. If a horse starts to develop symptoms, it is always considered a medical emergency. VetsterQuick tip: Keep a daily turnout routine that includes a five-minute field scan under and around oaks. If you see clusters of green acorns or storm-fallen branches, adjust turnout and clear the area before horses go out.What should you do immediately if you suspect acorn poisoning?Call your vet straight away; there is no antidote, and treatment is supportive with fluids, pain relief, and, if advised by your vet, activated charcoal or mineral oil administered professionally.Move the horse off pasture to a clean area with fresh water and palatable forage. Do not give activated charcoal or any other home remedy without veterinary instructionincorrect dosing or timing can complicate care. Be ready to tell your vet:When the horse was last on the affected paddockWhat youve observed (signs, colour of urine or faeces, appetite, behaviour)Any recent storms, changes in grazing, or known acorn fallsPro tip: Bag a small sample of the suspected acorns/leaves and take clear photos of the area under the oak. While not always necessary, this can help your vet assess the likely exposure.Post-crisis, monitor kidney and liver function as your vet advises. Recovery can be lengthy (often two months or more), so expect a careful return-to-normal plan with hydration, nutrition, and rest as priorities.How can you prevent acorn access in UK paddocks?Fence off oak trees to at least the branch span, clear falls promptly, and provide ample high-quality forage away from trees to reduce acorn-seeking behaviour.The BHS advises placing temporary electric fencing around oaksideally to the dripline (edge of the canopy)to keep horses off the heaviest fall zones. Pair this with proactive field management:Before turnout, do a quick walk of the oak line, especially after winds and storms.Rake or sweep up visible acorns and fresh leaf fall; prioritise green (unripe) acorns and young leaves.Relocate water and hay stations well away from trees to anchor horses in safer zones.Rotate fields to avoid overgrazing; rest paddocks that border oak-heavy hedgerows in peak months.Providing fibre is your best deterrent. Keep hay or haylage available during lean periods so horses arent tempted to browse oak material. When you need a safe, boredom-busting reward, choose purpose-made, additivecompliant treats. Our range of horse treats without risky botanicals gives you peace of mind during acorn season.At Just Horse Riders, we also recommend planning for a wet, windy autumn where turnout can be patchy. Reliable winter turnout rugs help you maintain a sensible turnout schedule without compromising comfort, so you can keep horses off highrisk areas when needed while still giving them time out.Are oak derivatives allowed in UK horse feeds and treats?Nooak parts are not approved feed additives. In the UK, only authorised additives under EC 1831/2003 may be used, and mixing additives requires appropriate registration with the Food Standards Agency.Under EC Regulation 1831/2003 (applied in the UK via national Feed Hygiene rules), preservatives such as propionic acid and other additives can be included only if specifically authorised for horses, at set maximum inclusion levels, and used exactly as directed. Feed businesses that mix additives or premixtures (vitamins, trace elements, preservatives) must register their activities with the Food Standards Agency. This framework helps ensure safety and traceability in the equine feed chain.For everyday horse owners, the take-home is simple:Buy reputable, labelled feeds and treats that comply with UK/EU additive rules.Avoid any product containing oak leaves, acorn fragments, or tannin-rich botanicals not authorised for equine feed.Contact the manufacturer if an ingredient seems unclear or unusual.Choose products from trusted brands and retailers. Our curated authorised supplements and carefully selected equine treats are sourced to comply with UK feed regulations, helping you avoid unwanted contaminants while supporting balanced nutrition through autumn and winter.What seasonal yard management helps reduce acorn risk?In autumn and early winter, manage grazing pressure, comfort, and routine with good rugs, clear paddocks, and consistent forage to minimise acorn temptation and stress.Autumn in the UK brings short days, slick ground, and frequent storms. A small shift in yard routine can keep horses comfortable and your field safer:Comfortable turnout encourages calm grazing away from trees. Consider waterproof, breathable turnout rugs that suit your horses clip and condition.When stabling overnight becomes necessary, match with cosy stable rugs for warmth while you plan early-morning field checks under oaks.When youre doing dawn or dusk acorn sweeps, increase visibility with hivis rider gear around the yard and lanes.Keep a tidy grooming routine after wet, muddy turnouts; a well-stocked grooming kit lets you spot subtle skin and mouth changes quickly.For hardworking rugs that stand up to British weather, browse proven options from WeatherBeeta to keep horses turned out comfortably while you fence or clear oak zones.Pro tip: Pencil in two storm response tasks on your yard board from September onwards(1) fence checks around oaks after high winds and (2) 15-minute acorn sweeps before next turnout. Turn a risky morning into a quick, repeatable routine.Our customers often tell us that planning hay placement 3050 metres away from known oak lines keeps the herd settled on safe ground and makes daily inspection of oak areas more manageable.FAQsAre small amounts of dried oak leaves in horse treats safe?No. While horses usually need a large quantity of oak material to cause toxicity, the tannins are undesirable even in small amounts. Avoid feeding any treats containing oak parts, and contact the manufacturer if you spot unusual botanicals. Choose purposemade, compliant options from our equine treats collection.What exactly causes oak poisoning in horses?Tannic and gallic acids in acorns, young leaves, buds, and bark damage the gastrointestinal lining, red blood cells, kidneys, and liver when eaten in sufficient amounts. Signs include inappetence, colic, diarrhoea, mouth ulcers, dehydration, and discoloured urine. For a welfare overview, see guidance from the British Horse Society.My field is overgrazedhow can I stop horses seeking acorns?Increase forage availability (hay/haylage) away from oaks, fence to the dripline, and rotate fields to reduce grazing pressure. Add safe, lowsugar rewards rather than allowing browsing under treesbrowse our safer treat optionsand keep water points far from oak lines so horses linger in cleaner zones.Is there a specific treatment or antidote for acorn poisoning?No. Vets provide supportive caretypically intravenous fluids, pain relief, and, where appropriate, professionally administered activated charcoal or mineral oil. Prognosis is guarded once clinical signs appear, and recovery can take two months or more. See veterinary guidance summarised by Vetster.When will my paddock be safe again after an acorn fall?Fields are generally safe by late autumn/early winter once trees stop dropping and youve cleared visible acorns and fresh leaf fall. Remain cautious in spring when tender buds and young leaves emerge, particularly if grazing is sparse.Some horses love acornscan they become hooked?Yes, some individuals develop a liking and will actively seek acorns regardless of available forage. For these horses, physical exclusion is essential: fence off oak areas to the branch span and maintain disciplined field checks, especially after storms.Whats the best way to clear fallen acorns quickly?Focus on high-density zones under the canopy. Rake or sweep daily during peak fall, prioritising green acorns and young leaves. For larger areas, a paddock sweeper or yard vacuum can speed things up. Pair clearance with fencing and strategic hay placement to keep horses occupied elsewhere.At Just Horse Riders, were here to help you navigate acorn season with confidence. From reliable turnout rugs and warm stable rugs to practical grooming essentials and compliant supplements, well support your plan to keep horses safe, comfortable, and out of the oak line this autumn and spring. Shop the Essentials Everything mentioned in this guide, ready to browse. Shop Turnout RugsShop Horse TreatsShop Stable RugsShop Hi-Vis GearShop Grooming Kit