The shelter accepted 110 animals in the first two weeks of the year after 147 were dropped off in December.

"That's going to be a huge jump if that continues" said shelter manager Nicole Balzer.

Kitten breeding season, which peaks in January before subsiding in autumn, delivered 53 kittens this month and 63 in December.

Forty-seven puppies have been given up in January so far after 28 were dropped off the month before.

Ms Balzer said the shelter did not usually see a large number of unwanted puppies given up after Christmas but rather a pre-Christmas spike in "teenage" dogs.

"Owners don't realise how expensive kennels are," she said.

"They don't realise how hard it is to get into a kennel at that time of year."

Ms Balzer said owners should build pet expenses into their holiday budgets.

For those people who want to help but "don't want to make the full commitment to an animal", Ms Balzer recommended becoming a foster carer to kittens and puppies.

Five foster carers have already signed up to look after animals until they have been desexed.

All the dogs and cats the RSPCA sells have been desexed, vaccinated, screened for diseases and treated for heartworm.

"You're mad buying a dog from a pet shop," Ms Balzer said.

The RSPCA euthanised 13,083 animals in the 2012-2013 financial year, about 2000 fewer than the year before.

The charity does not release the number of animals euthanised at each shelter.

NSW spokesman Lukas Picton said animals were put down if they were too sick or too badly behaved and that only rarely were kittens euthanised due to a lack of space.

All other animals stay with the RSPCA until they can be found a home.

"In some cases we have had animals that have been with us for hundreds of days," Mr Picton said.