Mrs Ball said they have an influx of unwanted kittens, many given for Christmas, around mid-February when school starts again.
She said if people are giving pets as gifts they should accompany it with a desexing and vaccination voucher.
NZ Veterinary Assocation spokesman Wayne Ricketts said a kitten or puppy can cost thousands over its lifetime and need daily nurturing and care.
"Think about how it will be looked after, when it will be de-sexed, vaccincations, health checks, how much it will cost on a daily basis and whether it will still be loved when it grows out of the cute kitten or puppy stage," said Dr Ricketts.
A cat costs an average of $466 a year in food, vet bills and healthcare and a dog more than twice that, $1047, as well as needing daily exercise and attention to behavioural problems.
Dr Ricketts said people should only buy pets at Christmas if they know they will be cared for responsibly.
"Too many unwanted pets end up in SPCA shelters and veterinary clinics as New Year turns into the work and school year."