"We are always prepared for these things at this time of year."
SPCA branches around the North Island said the biggest issues this summer were dogs left in cars and unwanted kittens and puppies.
Most people loved their pets, but they could make bad decisions about their care, said SPCA chief executive Ric Odom.
Desexing animals, especially cats, was a necessity for owners, he said.
"It's the responsible thing to do. We have such a problem in New Zealand with unwanted animals."
The advice about dogs and cars was simple: "Do not leave your animal in the car on a summer's day."
People might intend to be away from their car for only a short time, but there was every chance of being held up by any number of circumstances.
"Then they come back to find their pet severely distressed or worse."
All animals - but especially dogs - needed a lot of water and could easily overheat.
Mr Odom said most New Zealanders were responsible owners and some just needed a bit more petcare education.
"Most people treat their animals really, really well."
"And some of those that don't are not bad people. They just do not think," he said.NZME.