Effects of gonadectomy on scent-marking behavior of shelter dogs

Abstract

In male domestic dogs, castration appears to reduce frequency of sexually dimorphic behaviors, such as mounting and roaming, but results for urine-marking, another highly dimorphic behavior, are less clear. Using two different experimental designs, I studied effects of gonadectomy on scent-marking behavior during leash walks of dogs at two animal shelters in NY (Cortland Community SPCA and Tompkins County SPCA). In the between-dog study, I compared intact males and females and gonadectomized males and females with respect to rate of urination (a highly sexually dimorphic behavior), likelihood of ground-scratching (a somewhat sexually dimorphic behavior), and likelihood of defecation (a sexually monomorphic behavior). In my within-dog study, I compared rate of urination before and after gonadectomy in a subset of males and females. For the between-dog study, I found that castrated males urinated at lower rates than intact males and that spayed females and intact females urinated at similar rates; this pattern characterized dogs at both shelters. Gonadectomy did not influence likelihood of ground-scratching by either males or females at either shelter. For males and females at the Tompkins shelter and females at the Cortland shelter, gonadectomy did not influence likelihood of defecation. However, intact males were more likely to defecate than castrated males at the Cortland shelter. For dogs observed both before and after gonadectomy in the within-dog study, overall rates of urination decreased after castration in males but did not significantly change after spaying in females (sample sizes sufficient for analysis at the Cortland shelter only). Individual differences characterized male behavioral response to castration: while one male showed a very slight increase in mean rate of urination after castration (4%), the remaining sixteen males differed in degree of response, with percentage decreases in mean rate of urination after castration ranging from 14% to 72%. The source of this individual variation remains to be identified. In summary, spaying did not influence urination, ground-scratching, or defecation by female dogs. For male dogs, I found the most robust effects of castration on urine-marking, the most sexually dimorphic of the three scent-marking behaviors studied. This study is the first research based on direct observations of individual dogs to find decreased urine-marking by males after castration.