Acorns: the autumn field check worth doing today

The facts

Peak risk window

Acorns typically fall September to early November

Toxins

Gallic acid and tannic acid, found in acorns, oak leaves and oak branches

Organs affected

Liver, kidneys and intestines

Treatment

No specific antidote exists; care is supportive

How common

Acorn poisoning is rare in horses

Acorn poisoning in horses is rare, but it can be serious enough to kill. The toxins are gallic acid and tannic acid, and they are not only in the acorns. Oak leaves and oak branches carry them too, and the damage is done to the liver, kidneys and intestines.

Tolerance varies between individual horses, which makes the risk hard to predict. A few acorns are unlikely to trouble a horse who is also getting plenty of suitable high-fibre hay and grass. A large quantity can be toxic.

The only reliable protection is prevention, because there is no antidote. Treatment means managing the signs the horse is showing to limit organ damage, which can involve intravenous fluids to rehydrate and support the kidneys, electrolytes, and sometimes antibiotics. Badly affected horses may need hospital care.

One owner, Jodie Paylor, had her Welsh section A gelding Rocky taken to Pool House Equine Hospital in Lichfield with bloody liquid diarrhoea, colic-like signs, a heart rate above 100 beats per minute and dark urine. Testing confirmed toxicity. He was so dehydrated at one point that he could not lift his head, and she was told he might not survive the night. He was in hospital a week, came home on oral antibiotics, anti-inflammatory painkillers and a gut balancer, and made a full recovery. The field he had been in had an oak tree with acorn heads and some mouldy acorns beneath it. He was moved out of it. Notably, this happened earlier in the year, not in autumn.

What this means for you

Anyone grazing near oak

The safest option is to take horses out of any field with oak inside it or on the boundary. Fencing the tree off works only if the horse cannot lean over or reach under the fence.

Owners with no oak in the field

Oaks nearby still matter. Leaves, branches and acorns blow in during windy weather, so the check does not end at your own hedge line.

Owners of horses on bare grazing

In Jodie Paylor's case there was little grass in the field, and the pony picked the acorns out. Sparse grazing and fallen acorns are a poor combination.

Anyone spotting symptoms

Depression, loss of appetite, dehydration, mouth ulcers, colic and constipation are listed signs. Diarrhoea, bloody urine and nervous system problems point to more serious illness.

What to do

1. Walk the field boundary and look for oak inside it, on the perimeter and in neighbouring land

   Now, during the September to early November fall

2. If oak is present, move the horses out, or fence the tree so the horse cannot reach under or lean over

   Before the next windy spell

3. Re-check the grazing regularly for leaves, branches and acorns blown in

   Ongoing through autumn

4. Learn the symptom list and call your vet early if you see colic signs, diarrhoea or dark urine in a horse with acorn access

   Immediately