However, the canine team leader believes it was most likely the puppies were dumped that morning because they had been fed before being left.
The puppies were immediately taken into the SPCA centre to be fed and checked over - luckily, all were healthy.
"If it wasn't for Mac's persistence the puppies would have been missed for sure, and no one would have known until they started to decay," Joanna said.
"The bag was tucked right in a corner under some overgrown grass and branches," she said.
It's common for rubbish to be dumped on the road near the Hastings SPCA and Joanna said the reusable shopping bag looked as if the wind had blown it into the bush.
Fortunately, the puppies were brought indoors half an hour before Hastings had one of its heaviest hailstorms of the year.
"They would not have made it through that hailstorm if they were still outside," Joanna said.
Since being found, the seven pups have gone to three foster homes and are in safe hands.
The bag of puppies was dumped about 30m from the SPCA's front door, Joanna explained.
"If they had just come in and seen us we would have helped them," she said.
The Hastings centre would not only have taken the puppies, but would have offered more help for the mother dog.
Joanna said the SPCA often will take in the mum and pups while she is still feeding them and then give the mother back to the owners once the puppies reach an appropriate age to be separated from the mother dog.
The SPCA wants to spread awareness that if people need help with desexing, to "get in touch with us as we can help with desexing vouchers".