The death of more than 20 horses and the discovery of eight emaciated animals on a Queensland property is "beyond comprehension" according to an animal rescue group which has offered to foster the surviving animals.
Authorities have identified seven former race horses among the dead animals on the property.
Biosecurity Queensland says inspectors and a vet visited the property in the Gowrie Mountain area, in Toowoomba west of Brisbane following complaints, and directed the horses' owner to feed them.
The response to the deaths so far has been "totally unacceptable" according to the founder of Australian Farm Animal Rescue Matters, Marjorie Pagani.
When the animals were fed following complaints last week Ms Pagani says the horses were given "mouldy garden mulch".
"They're in acres of dirt, we have foster carers ready to help," Ms Pagani said.
She said the department of agriculture took more than five days to visit the horses, in which time one animal died.
The remaining eight horses are on the brink of death and in need of treatment, she said.
Biosecurity Queensland said it could not make further public comment on the matter while this is an active investigation.
Queensland Racing Integrity Commission Ross Barnett said the owner of the horses is not and has not been a licensed racing industry participant.
But race horses were found among the dead.
"Among the deceased and horses in serious condition seven can be identified as ex race horses," Mr Barnett said.
The matter has also been reported to the RSPCA.