Salivary oxytocin in pigs, cattle, and goats during positive human-animal interactions

Research on oxytocin (OT) has provided crucial insight into the neuroendocrine mechanisms of social behavior and human-animal interactions. Nonetheless, this peptide hormone remains challenging to sample, usually requiring invasive measures in the brain or blood, which limits its use. We conducted an analytical validation of the measurement of OT in the saliva of three common farm animal species: pigs, cattle and goats. We then investigated the biological significance of salivary OT concentrations by using a positive human-animal interaction paradigm. The paradigm varied in terms of human familiarity and included a control condition where the animal was alone in the testing pen. A total of 18 pigs, 18 cattle and 9 goats were subjected to each condition using a within-individual counterbalanced design. Animals were free to choose to interact with the human. Saliva samples were collected immediately before and after the 10-min test, and behavior during the test was analyzed. Oxytocin could be reliably measured by ELISA in the saliva of goats (without extraction), and in the saliva of pigs and cattle after extraction. Salivary OT concentration did not change consistently according to testing condition. However, salivary OT concentration was significantly associated with some behaviors, with different relationships depending on the species. In conclusion, OT can be reliably measured in the saliva of goats and, after extraction, in the saliva of pigs and cattle. The relationships of OT with human-animal interactions and animal behavior were complex and to some extent species-dependent, possibly reflecting the perception of the interaction by the animal.