At what age should I get my pet sterilised? Cats can become pregnant as early as 4 months old, so RSPCA recommends getting your cat desexed early, to prevent unwanted pregnancies. RSPCA WA sterilised kittens from 8 weeks old. Dogs can become pregnant as early as 6 months old. While RSPCA recommends early sterilisation for dogs, your vet will be able to provide the best advice for your circumstances, and your particular dog. Your vet will factor in general desexing advice and any breed-related considerations. In Western Australia, sterilisation of cats is mandatory by 6-months old, under section 18 of the Cat Act 2011. When the Dog Amendment (Stop Puppy Farming) Bill 2021 becomes law, it will be mandatory to sterilise your dog by the time they are 2-years-old, unless they are exempt.