The RSPCA is appealing for the owner of 22 horses left in a field in Watford to come forward after one horse died and another two were found collapsed.
The RSPCA removed the dead body, the two collapsed horses and a third live horse from the field off Hamper Mill Lane, Watford on Friday 19 December.
Seven other horses were removed by bailiffs earlier in the week at the request of the owner of the field, where the horses had been left without permission.
The charity said the horses are being examined and the emaciated body of the dead one will be post-mortemed to establish a cause of death.
The three live horses are also extremely thin, but the cause of the weight loss is currently unknown.
As spokesman said: “The remaining 18 horses are in reasonable bodily condition and the RSPCA will continue to make further visits to the field to monitor them.”
RSPCA inspector James Bromley said: “We are currently investigating how these four horses came to be in such a poor condition. There may be a reasonable explanation so we need to find the owner as soon as possible to rule them out of our investigation.”
Anyone with information about this incident should call the RSPCA on 0300 1234 999.