Visitors are being urged not to feed semi-wild ponies on Dartmoor because it is making them unwell and causing "unnecessary issues".
The Dartmoor Livestock Protection Society said the animals now wait in car parks in the national park in Devon expecting to be fed. This is leading to health conditions such as colic, which can cause abdominal pain.
Dartmoor National Park said it is illegal for people to feed the animals, and if it continues, people could be charged under the Animal Welfare Act.
Karla McKechnie, Dartmoor livestock protection officer, said along with the health issues, ponies being fed by visitors could increase the risk of them being struck by vehicles.
McKechnie said 25 ponies had been hit on roads this year, resulting in 18 deaths.
"Ponies relate roads to cars, cars to people and people to food," McKechnie said.
"So potentially they're sitting ducks by the side of the road."
McKechnie said "many ponies" had fallen ill over the years due to food they had been given to eat by visitors.
She said she had seen a family feeding ponies ham sandwiches, which she said was food the animals should not eat.
"I explained what the situation could be, the potential problems and they nodded at me as if they agreed with what I was saying," McKechnie said.
But she said after she turned away, the family threw the food on the floor and ran off laughing.
"You just can't compete with that… I don't know how you get the message across," she added.
McKechnie said getting food from visitors could also lead to ponies "turning aggressive" if they stopped being given the items.
McKechnie added she had seen pictures and videos on social media of ponies sticking their heads into cars.
She asked people visiting Dartmoor to appreciate the ponies.
"Don't feed them and don't pet them," McKechnie said.
"Otherwise it'll be me that's going out in the middle of the night to have to deal with a pony which potentially has to be put down."
Equine veterinary surgeon Jess MacPhail said horses and ponies had a "sensitive digestive system".
Visitors Urged Not to Feed Dartmoor Ponies Over Welfare Fears