Differences in serotonin serum concentration between aggressive English cocker spaniels and aggressive dogs of other breeds

Aggression is one of the most common behavioral problems in dogs and may have important negative effects on public health, human–animal bond, and animal welfare. There is ample evidence showing a negative correlation between serum serotonin concentration and aggressive behavior in a variety of species, including the domestic dogs. This negative correlation is particularly pronounced in dogs that show impulsive aggression. Data obtained in some previous studies suggest that the English cocker spaniel (ECS) is more likely to show impulsive aggression than other breeds. Therefore, the aim of this study was to analyze possible differences in serum serotonin levels between aggressive ECS and aggressive dogs of other breeds. Nineteen ECSs presented for aggression at the Animal Behavior Service (School of Veterinary Science, Barcelona, Spain) were evaluated and compared with 20 aggressive dogs of other breeds attended at the same center. Serum serotonin levels were measured using an enzyme-linked immunosorbent assay method. Statistical analysis was done using the SPSS 15.0 for Windows. Aggressive ECSs had significantly (P < 0.001) lower levels of serum serotonin than aggressive dogs of other breeds (318.6 ± 67.1 and 852.77 ± 100.58 ng/mL, respectively). Variances were not significantly different between ECSs and other breeds (standard deviation = 449.84 ng/mL vs. 292.47 ng/mL, P > 0.05). This finding may explain why ECSs are more likely to show impulsive aggression than other breeds, and suggests that the ECS could be a good model to study the neurophysiologic mechanisms underlying impulsive aggression.