A black five-year-old mare had to be put to sleep after being found dumped “half dead” in a remote Surrey lane last week (27 January).
The cob was found by a walker, who said she was so thin and weak she was unable to stand up.
“This poor horse was in a very bad way. She had just been left there, suffering,” said RSPCA inspector Rebecca Carter.
The mare had a severe case of redworm and officers believe she had been lying on the ground for some time.
The bruising around her mouth suggested she had been been dragged to the secluded spot in her collapsed state.
The RSPCA inspector said the man who found the mare mistook her for a log at first, as she was so weak and still.
A vet was called out but said nothing could be done to save the horse. She was put to sleep to end her suffering.
The horse was found to have an acute case of cyathostomias, a condition which causes severe diarrhoea and dehydration.
The disease, caused by redworm, affects horses of all ages but is commonest in those under six years of age.
The RSPCA said the disease is one of the major issues it finds in horse neglect cases and can often be fatal.
“The condition is easily treated if caught in time which makes cases like this seem so pointless and extra cruel as they are so easy to avoid,” said Ms Carter.
She spent some time with the horse while waiting for the vet and said the mare was very affectionate and even tried to follow her even though she was too weak to get up.
“She was a real sweetheart — it was just so terribly sad,” she added.
The RSPCA is appealing for anyone with any information to contact them on 0300 123 8018.