RSPCA Cymru is appealing for information after finding an “extremely thin” pony on Gelligaer Common.
Concerns were made for the pony, believed to be an older adult, on Thursday, January 30.
The animal has since been taken into RSPCA care.
RSPCA inspector Christine McNeil said: “This pony was found to be in extremely thin condition and also had some dental issues.
“As she had no microchip it’s impossible for us to trace her owner at this time. I’m hoping that someone will know who she belongs to, or have seen something that might help us to trace the person or people who owned this poor pony.
“Anyone with any information should call us on our inspector appeal line 0300 123 8018 and ask to leave a message for me.”