Most unspayed female cats experience heat cycles during ten months of the year. While in heat, many cats writhe and yowl–loudly and continually–at all hours of the day and night. By eliminating the heat cycle, spaying frees cats (and their human companions) from considerable stress.
Most unneutered male cats frequently spray urine – for example, on furniture and walls – to mark territory. In contrast, only one in ten neutered males sprays. The urine of an unneutered male cat has an exceptionally strong odor. Neutering male cats at an early age usually eliminates this unpleasant behavior.
Spaying female dogs prevents the irritability and aggressiveness that some dogs show while in heat.
In many male dogs, neutering reduces or eliminates sexual mounting behavior and territorial urine-marking (including any taking place inside the house) especially when animals are neutered at an early age.