Why does my pet need to be sterilised to enrol in the program? Unsterilised animals are a risk because of their potential to breed; and they are the reason why so many unwanted animals end up in shelters. Unsterilised animals are also at greater risk of certain illnesses and diseases, and they generally have more behavioural problems than animals who have been sterilised. Most of our foster carers are animal lovers with pets of their own, so it’s unfair to place an unsterilised animal in their home. By law, all cats in Western Australia over the age of 6 months must be sterilised; and the government is in the process of tightening laws around dog sterilisation.