Opioid systems are implicated in social attachment processes. This research sought to determine the functional contribution of each opioid receptor in modulating social attachment/separation distress. Following ICV administration of opiate probes, 7-day-old cockerels were isolated from conspecifics for a 3min test period under either a mirror or no-mirror condition. Vocalizations served as the measure of separation-stress. Opioid receptor probes included: the μ agonist DAMGO (0.02, 0.19, 1.95nmol), the μ antagonist CTOP (0.009, 0.09, 0.9nmol), the δ agonist SNC80 (0.3, 1.0, 3.0μmol), the δ antagonist naltrindole (0.2, 2.2, 22.2nmol), the κ agonist U50, 488 (1, 30, 100nmol), the κ antagonist norBNI (1.3, 13.6, 136.1nmol), the NOP agonist N/OFQ (0.01, 0.1, 1.0nmol), and the NOP antagonist UFP-101 (0.1, 1.0, 10.0nmol). DAMGO attenuated separation distress vocalizations. No other drug probe enhanced or attenuated distress vocalizations. Further, the non-selective opiate antagonist naloxone (0.3, 8.3, 27.5nmol) did not exacerbate distress vocalizations. These results suggest that only the μ receptor modulates social attachment in young domestic fowl.