The gonad chronicles, part 2: Veterinary research explores neutering's elusive impact
This is the second article of a two-part dvm360 series focusing on neutering and the effect of hormones on the development of both physical and behavioral concerns ((see the Related Links section below for a link to part 1). We will explore the relevant data demystifying the connection between hormones, behavior and health.
That said, both neutered and intact dogs may exhibit behavioral concerns, and only some of these concerns are affected by sexual dimorphism. Dimorphic behaviors associated with the presence of testosterone include urine marking with lifted leg, roaming and some types of mounting. Mounting is an unclear issue because it occurs in a number of contexts, most of which are not sexual, and both sexes do it. Castration results in an androgen drop within six hours, and most hormones that decrease do so within 72 hours.2In the 1976 Hopkins study, which looked at male behavioral patterns and the effect of castration, roaming decreased by approximapattely 90 percent, male-to-male aggression by approximately 75 percent, urine marking by approximately 60 percent and mounting by 80 percent in male dogs that were neutered. However, marking, mounting and fighting are complex behaviors not wholly controlled by hormones. There is a significant learning component involved in practicing these behaviors that won't be redressed by castration. Context also matters, so space and social interactions need to be considered. Finally, no distinction is made between normal and pathological behaviors, and one might expect castration to affect them differently.
Researchers have paid less attention to the role of female sex hormones and aggressive behavior, but one study has made a connection within a fairly restricted population.3 Only female puppies that were already showing signs of "dominance aggression" became worse after spaying. Spaying had no effect on any other age and behavior group combinations.4 It is possible that for these young, aggressive bitches, sex hormones play a helpful role in modulating their reactivity. If these dogs are in responsible households where breeding is prohibited, allowing them to have a heat cycle may be beneficial in terms of ameliorating their aggression, but there is little data on this.