Councillors voted unanimously in favour of the measure at a meeting last week.

Cats Crisis Coalition director Carole Webb said anyone with doubts on whether desexing was the right move should visit their local animal shelter.

"If you see how many cats are coming in on a daily basis and having to be put to sleep, it's heartbreaking. Desexing will prevent unwanted cats, which will stop them becoming stray or going to the shelters."

The council will introduce mandatory desexing for cats being registered for the first time after April 2010.

Ms Webb said, on average, four kittens were born per litter and each cat could produce three litters a year.

"Yarra Ranges is a rural environment and cats are more likely to disrupt the wildlife. People do need to be educated, but we have tried that and we are not seeing the impact at the shelters."

Debra Boland, of Coldstream Animal Aid, said it often took owners more than a week to find their missing cat.

"Only 11 per cent of cats are returned to their owners but a large number are unowned despite depending on people for survival. Eighty-nine per cent of cats are unclaimed and around 55per cent are euthanased after eight days because of their temperament.

"Year after year, we put out the message in the hope there is a reduction in our intake, but it isn't getting any better. If anything, it's getting worse."

The vote was part of council's domestic animal management plan, adopted in October last year, which recognises cat over-population as a major problem.

Mayor Len Cox supports the proposals. "I don't think it's cruel. It is more cruel not to desex a cat and then not take care of it or any kittens. I think responsible cat owners will understand what council is trying to do."