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Peter Nicholl, a vet at Earlwood Animal Hospital, removed the suspicious item from the animal, which ingested it at Bardwell Valley, in the city’s south, this week.
Nicholl said he has since been made aware of a similar incident around “eight kilometres away” in Sydney Park, in the Inner West.
He fears a green substance found inside the sac, which appears to be an animal part, may be poisonous – and may have been left deliberately.
“At the moment I would not be walking my dog off lead,” he told 9news.com.au, adding the dog he treated made a full recovery.
“The dog had swallowed it whole and the owner got in early enough.
“We were able to make it vomit and it hadn’t been digested.
“We don’t know if there’s any poison in them, it’s very likely that there is.”
Nicholls said it’s unlikely confirmation will come, as “toxicology on things like this is incredibly expensive”.
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“If they want to test for multiple things it could cost many thousands of dollars to do so,” he said.
“People have to got to be aware and make sure dogs are on their lead, so they don’t have a chance to go and ingest them.
“And keep your eyes out, the dog will notice them before you will.”
This could be one of the next animals to go extinct
Nicholl said if a dog does eat one of the objects, time is of the essence.
“You have less than an hour (before digestion starts),” he said.
”As soon as it happens, you should try and get to one of your local vets.
“If none of those are open, it’s late at night, you need to get to one of the specialist centres.
“Vets have a medication they can administer to the dogs to make them bring it up.”