Carolle Lee-Jones from Bridgnorth keeps her ponies at the Eardington Nature Reserve.
But a couple of weeks ago pony Peggy passed away after her body couldn't cope with the sugar overload from carrots and other food she had been given by well meaning visitors to the reserve.
Another of her ponies is also on medication for complications after becoming obese.
"We have asked so many people not to feed the ponies and have put signs up at the reserve. But they still insist on bringing carrots and other food for them."
She said the hardy Welsh mountain ponies were genetically used to being outside in the winter and should look lean at this time of year.
"Their bodies can then deal with the sweet, spring grass that is now growing," she said.
"They are fed a special diet and, if they have too much food, their metabolism can't deal with it. They can't process the excess sugar and this can lead to kidney and liver problems."
The death of Peggy left Carolle's son, eight-year-old Archie, heartbroken.
"He shows and rides the ponies and is devastated," Carolle said.
It has also left Peggy's pony mate, Solo completely lost. The family have managed to find another pony who will be at the reserve to keep Solo company this week.
"We would just appeal to people to enjoy looking at the ponies but please, please don't feed them, whether at Eardington or wherever they are."
"Solo also became overweight and is no on a special liver tonic."