Comparison of anesthesia with isoflurane or sevoflurane and sedation with diazepam for branding of juvenile grey seals (Halichoerus grypus)

Hot-iron branding has been used successfully as an identification means for long-term population studies in pinnipeds. To decrease the stress associated with this controversial procedure, two anesthetic systems adapted for... [ view full abstract ]

Hot-iron branding has been used successfully as an identification means for long-term population studies in pinnipeds. To decrease the stress associated with this controversial procedure, two anesthetic systems adapted for field conditions (outdoor temperature = -10 to 0 °C.) were compared with a standard sedation protocol. We hypothesized that anesthesia of juvenile grey seals for branding with these systems would not increase the handling time but would reduce struggling when compared to the sedation protocol. Manually restrained seals (≈50 kg) were anesthetized using either sevoflurane (2-3ml) in an open anesthetic system (SEVO, n=12) or isoflurane (≈5%) vaporized with ambient air (ISO, n=7). Intravenous diazepam (10mg) was administered to the control group (DIAZ, n=9). Induction/injection time and duration of morphological measurements and branding were compared between treatments. Induction time was shorter (p=0.046) in the ISO group compared to the SEVO group. Time needed for branding was significantly longer for the DIAZ group compared with the ISO (p=0.0083) and SEVO (p<0.0001) groups. No difference was observed between the total duration of the procedure in the three groups. Transient periods of apnea and CO2 rebreathing were observed in the SEVO and ISO groups, but all seals recovered well. General anesthesia decreased the needs for physical contention, hence reducing animal struggling and risk of injuries to handlers. The anesthetic systems used were compact and easy to transport to remote locations. Anesthetic techniques described here should be preferred over sedative protocols for moderately invasive and short procedures such as hot-iron branding.