A mare in foal with severe ragwort poisoning been taken in by the Essex Horse and Pony Protection Society.
Lois and her yearling, Mitch, were reported to the charity by a member of the public from Aveley, Essex, last month.
The mare and yearling were turned out in a large area by the M25 junction with Aveley on the A13. They were able to get onto the road from there.
She had ragwort poisioning so severe that it had led to serious photosensitivity, meaning she burnt badly in the sun.
“Bald areas of her skin were badly inflamed and the skin was peeling off,” said a spokesman for the organisation. “She was in a sorry state and her skin had turned hard and leathery where she had lost her hair.
“Our vets diagnosed photosensitivity and the condition is drastically improving with the proper care and treatment.
“Lois had a yearling colt at foot and is also in foal — the birth being imminent.
“Lois has lost 70% of her liver function and our vets are surprised she is still alive.”
The mare is “still not out of the woods” but her skin condition is improving.
“In the meantime, she wears a UV mask and rug when out and has medication to help her skin heal,” added the spokesman.
Mitch has been gelded by the charity’s vets and is now in a paddock with other geldings of his own age.
“Our policy is not to put horses on loan until they are at least four years old,” added the spokesman. “Mitch will learn how to play and integrate with a herd over the next couple of years and when he is physically and mentally ready, we shall start the backing process in readiness of finding him a suitable loan home. He still has some years to go yet.
“If Lois survives her ordeal, we shall eventually look to place her in a suitable foster home but that will not be until her foal is weaned and off hand and she is ready.”
Owners are warned to be aware of the dangers of ragwort, as Lois is the second mare in a month to suffer from photosensitivity due to liver damage caused by the poisonous plant.
The other mare was found on 4 June with a group of other horses in Maidstone, Kent, and was rescued by the RSPCA.
The owners have not been traced. She is estimated to be around three years old and her condition was so severe she needed removing from the sun immediately.