Below is an enlightening post from Victoria Stilwell’s blog about a 1997 study conducted by researchers at the University of California, Davis, Veterinary Medical Teaching Hospital found.
Misbehaving Male Dogs
This study evaluated how neutering adult male dogs affected such problem behaviors as urine marking in the house, mounting, roaming, fear of inanimate stimuli as well as aggression toward family members, strangers, household dogs, unfamiliar dogs and human territorial intruders.
Fifty-seven dogs that had exhibited one or more of these problems before being castrated at 2 to 7 years of age were included in the study.
Follow-up revealed that castration was most effective at reducing:
• urine marking
The decrease was marked.
• These behaviors decreased by 90% in 40% of the study dogs
• And decreased by 50% in the remaining 60% of the study dogs
No relationship existed between the effect of neutering and the age of the dog or duration of the problem behavior before castration.
Neutering also affected aggression toward canine and human family members but to a lesser extent and in fewer dogs, with 25% of the study dogs improving by more than 50%.
Surprisingly, 10% to 15% of dogs showed less aggression toward unfamiliar dogs and territorial intruders. Therefore, neutering can likely provide marked improvement for many dogs that are exhibiting marking, roaming or mounting behavior and may offer some improvement in dogs that are aggressive toward people and other dogs. Neutering seems to be less successful in reducing other types of aggression, although improvement is possible.
Misbehaving Male Cats
For cats, the story may be even more promising. “Regarding behaviors that are more specific to male animals, castration seems to be more effective [in modifying behavior problems] in cats than in dogs,” says Melissa Bain, DVM, assistant professor of clinical animal behavior at UC Davis.
A study conducted at UC Davis in the 1990s found that in 90% of male cats, castration greatly reduces or eliminates
• urine spraying
• fighting with neighborhood males
Fifty percent of the cats showed a dramatic decrease (80% decrease) in the spraying, roaming and fighting in the first week, although the remaining study cats demonstrated a more gradual decline.