Neutering male cats makes them less likely to spray and makes male dogs less aggressive and less likely to bite. Spayed females do not go into heat. A female in heat can be noisy, temperamental and attract unwanted males. Neutered males will not stray, looking for a female in heat. Females spayed before their first heat are healthier than those that have a litter.
Many shelters now sterilize dogs and cats when they are only two months old.
Animals that have been spayed or neutered are less likely to develop reproductive cancers - one of the most common causes of death in an animal. Animals do not have any conscious understanding of their sexual identity and so will not feel deprived if they are spayed or neutered. Almost all animals recover from the operation in a day and do not seem to notice that anything has happened to them. Dogs do not get fat and lazy as a result of being spayed or neutered. Pets gain weight for the same reason people do - too much food and not enough exercise.