Hundreds of extra pigs sent out into New Forest as dry summer produces millions of nuts which are toxic to livestock

If you go down to the woods today you may be in for a big surprise. Not from teddy bears, but from an army of pigs snaffling up a bumper crop of acorns.

The mild spring and largely dry summer has yielded a glut of millions of green acorns, or oak nuts, in the New Forest in Hampshire.

They are poisonous to ponies and cattle but not to pigs, which have for centuries been let loose to get to them before they harm other animals – a practice known as "pannage".

Usually only about 200 pigs are needed to polish off the nuts but this autumn 500 have been released two weeks early to cope with the glut. They will spend the next 60 days munching the acorns before being rounded up in November.

Jonathan Gerrelli, the forest's head agister – an official who manages the commoners who have ancient grazing rights – said: "Acorns are poisonous to ponies and cattle. If they eat them they tend to start to bleed internally and then die a horrible death.

"But for some reason they are not toxic to pigs, and at this time of year the New Forest pigs have a field day.

"We've started pannage earlier than usual. This is simply because there is a very large crop of acorns that are falling earlier due to the sheer weight.

"You can see that the trees are loaded with them this year, the branches are hanging down under the weight. It must be because we had a prolonged dry spell over the summer."

In the 19th century 6,000 pigs were regularly turned out for pannage. As well as saving the ponies and cattle, pannage also fattens up the pigs for slaughter.

Nigel Taylor, head of horticulture at the Royal Botanic Gardens in Kew, said: "It has been a good year for oak trees and acorns in southern England. We had no late frosts this year to damage the young structures that become acorns.

"When you have a period of not much rain but a great deal of sun and light, that then leads to more energy in the trees and more acorns."