Rescue centres say they are being swamped by unwanted kittens.
Bristol Dogs and Cats Home is full with more than 30 homeless cats, including a box of kittens that were dumped outside the centre's front door.
This time of year is known as "kitten season" as the number of animals being handed in increases dramatically.
Experts are advising pet owners to have their female cats neutered to prevent them having unwanted litters of kittens.
Lee Coombs, of the Bristol Dogs and Cats Home, said: "There is also a long waiting list for people who want to hand their cats and kittens over for rehoming."
He said there were special low-cost schemes for cats to be neutered.
He added: "There really is no excuse to end up with unwanted animals and dump them on our doorstep in a box. It is disgusting behaviour."