August 31, 2017

Audience: Executive Leadership, Shelter/Rescue Staff & Volunteers, Veterinary Team

Organization: Colorado State University
Investigator(s): Rebecca Ruch-Gallie and Stephen Pannone
Grant Amount: $5,500
Project Type: Summer Scholar
Project Status: Research Complete

Project Summary

This Colorado State University summer scholar study aimed to determine and compare 5-HT (serotonin) concentrations in pit bull-type dogs, who would be subject to breed restrictions, and non-pit bull-type dogs entering northern Colorado shelters. The results indicated no significant difference (P=0.085) in average 5-HT serotonin levels between pit bull-type and non-pit bull-type dogs.


To examine whether all pit bulls regardless of temperament are biochemically predisposed to aggressive behavior due to a deficiency in serotonin


Study participants were divided into two groups: pit bull-type and non-pit bull-type. Grouping was determined by phenotypic appearance, as this is the same criteria used by the City of Denver to enforce breed ban legislation. Thirty pit bull-type dogs and 44 non-pit bull-type dogs were pre-screened using information from the three participating shelters' databases in PetPoint. Dogs had similar demographic characteristics and length of time spent in shelters (average LOS was 4.7 days). All dogs had to have scored an average of 1's with no score higher than a 2 upon SAFER evaluation. Puppies and seemingly older dogs were excluded in order to study dogs within similar estimated age range; and there were approximately same number of males and females. Blood samples were drawn from pre-screened dogs either through jugular or cephalic venipuncture at the shelter. Serum samples were analyzed using the Serotonin ELISA kit from Eagle Bioscience.


  • There was no significant difference (P=0.085) in average 5-HT serotonin levels between pit bull-type and non-pit bull-type dogs. Mean serum serotonin concentrations of pit bull-types was 432 ng/ml and non-pit bull-types was 533.4 ng/ml.
  • Interestingly, there was a significant difference between the very large and the very small dogs in the study (requires more research).


Based on this data, there is a lack of evidence indicating that there is a significant difference between mean serotonin levels of pit bull-type dogs compared to non-pit bull-type dogs. However a larger sample size is needed to determine the true significance of these findings. The addition of a weight requirement for future study participants may help to reduce some confounding factors.