Animal Justice Party lead senate candidate Darren Brollo and Hunter Horse Haven spokesperson Deb Barber say the RSPCA left 17-year-old retired racehorse Jet in a poor condition on the Weston property for too long before the owner surrendered him to the Anna Bay equine refuge.

But the RSPCA said Mr Brollo had "misrepresented and omitted information, and has failed in his due diligence to ascertain the facts of the matter".

Ms Barber, who has been caring for Jet around the clock, said the horse was so malnourished he was eating his own faeces.

"Chronically starved horses are sometimes known to eat their own droppings and Jet even tries to get it back from us as we collect it," she said.

"He has someone with him 24 hours a day, but it's still touch and go at the moment and will be for some time. He has multiple health concerns, with the most upsetting one that he has a grade five to six systolic heart murmur, with grade six being the very worst.

"In some chronically starved horses with a heart murmur we can provide some healing with weight but I seriously doubt this one will."

Mr Brollo said the case showed ongoing problems with ensuring safe re-homing of retired racehorses.

He said the RSPCA's response was "unacceptable" and called for the establishment of an independent office of animal protection.

"Australians are tired of animal cruelty going unreported and unpunished," he said.

An RSPCA spokesperson said the agency "unequivocally denies" the allegation that Jet was left to starve for 12 months.

The spokesperson said the RSPCA worked with Jet's owner over the period to improve his well-being, conducting several checks of two horses to ensure their condition was improving, which the agency believed was the case.

The spokesperson said the owner complied with directions to seek vet assistance and to put a feed plan in place but Jet's condition "drastically deteriorated" after a check on March 4 - and the owner did not contact RSPCA for help.

"RSPCA NSW is deeply saddened and disappointed that we were not contacted for help, as the inspectorate has been consistent and persistent with offers for assistance and has clearly communicated that surrender was always an option," RSPCA said.

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