Helen Matthews said it took three people to pull the dog from her horse after it tore a 30-centimetre piece of flesh from its stomach and groin on Anzac Day.
Ms Matthews was worried the dog could kill a child and said people who owned the breed needed to socialise their dogs and properly restrain them.
"If this had been a child or small dog it would have been a different story," Ms Matthews said.
"I felt physically sick. My main concern was that I was very nervous about the dog getting back out again so I called the police [after the attack]."
A Sutherland Shire Council spokeswoman said the dog was seized and remained impounded as the owner had not returned messages left by rangers.
"The dog attacked a Shetland pony, inflicting substantial injuries to its mouth, neck and groin area, which required treatment by a vet," the spokeswoman said.
Council officers determined there was inadequate fencing where the dog was housed.
"The attack was witnessed by a number of people and statements have been obtained from most of them, with the exception of the dog's owner. Unfortunately a number of messages have been left with the dog owner but, as yet, he has not responded."
The spokeswoman said the dog was not registered or recorded as living with the owner and said if the owner wished for it to be returned the council would declare the dog dangerous.
"Should the dog not comply with the dangerous dog control requirements [the] council can take further action if deemed necessary in the interest of public safety," she said.
The dog's owner will face a maximum court fine of $5500 over the attack.
He would also face fines of up to $880 for the offences of not registering his dog and not notifying the council of a change in registration details.
(The Leader - May 13, 2013)
