Investigating Targeted and Untargeted Approaches to Biomarker Discovery in Fearful, Adult Dogs

Lay Summary

Chronic fear and anxiety experienced by pet dogs can negatively affect their welfare, although the physiological mechanisms underlying these states remain poorly understood. The objective of this study was to explore metabolites associated with fearfulness in dogs. Blood was collected from 100 adult dogs fed a standardized diet, and owners were asked to complete two surveys about their dogs’ behavior, and links between blood measures and survey scores were then examined. Using metabolomics, touch sensitivity in dogs was associated with tryptophan metabolism, a pathway involved in serotonin synthesis. Further, dog-directed fear, or fear of other dogs, was associated with pyrimidine metabolism, a pathway involved in nucleotide synthesis. Two individual metabolites also stood out: formiminoglutamic acid, which is related to folate/one‑carbon metabolism, was higher in more fearful dogs, and lauric acid, a medium‑chain fatty acid, was higher in dogs with greater touch sensitivity. In more targeted analyses of the serotonin system, a higher ratio of serotonin’s breakdown product (5‑hydroxyindoleacetic acid) to serotonin was associated with fewer separation‑related behaviors, whereas serotonin alone was not clearly associated with any behavioral measure. Overall, these exploratory findings highlight biologically plausible pathways, particularly those involving tryptophan, folate‑related one‑carbon metabolism, and lipids, that could inform future nutritional or medical strategies for dogs with fear‑related problems.