Abstract

Currently, rectal temperature is the method of choice employed by the U.S. Navy Marine Mammal Program (MMP) to measure the core body temperature of marine mammals. While this method provides a suitable measurement of core body temperature, it is not considered a practical method of temperature assessment while animals are operational due to interruptions of animal task performance.

Materials

Alternative methods of temperature assessment currently available include esophageal probes, ingestible sensors, implantable probes and infrared thermometers. Investigations of the available methods of temperature assessment were conducted and two temperature monitoring systems were selected for study based on product design and feasibility of use. The two systems selected were CorTemp, an ingestible temperature probe system marketed by HQ Inc., and Bio-Thermo microchips, an implantable microchip system with identification and temperature sensing capabilities, created by Destron Fearing and marketed by Digital Angel Corporation. Initial trials for both of these systems focused on the safety and feasibility of use in California sea lions and bottlenose dolphins.

Special modifications were made to both systems to make them appropriate for use with the bottlenose dolphins and California sea lions involved in the study. Modifications to the Bio-Thermo system included increasing the reading depth of the microchip reader for use with both species, and designing a new delivery system for the microchip with longer needles for use in bottlenose dolphins. The CorTemp system offers a range of ingestible sensor sizes for different animal species. The human pill was selected for the California sea lion trials and was expected to pass through the entire gastrointestinal tract. The porcine pill was selected for use with the bottlenose dolphin and was expected to remain in the stomach and not pass through the rest of the gastrointestinal tract. The only modification to the CorTemp system was the addition of loops of suture to the ends of the porcine sensors in case there was a need to remove them endoscopically from the dolphin's stomachs.

Methods

A small population of California sea lions and bottlenose dolphins were selected for the initial safety trials involving both temperature systems. Throughout the initial trials, animals were monitored for any adverse reactions to the temperature monitoring systems. Animals receiving ingestible probes were monitored for lethargy, vomiting, inappetance, signs of abdominal pain and any other changes in behavior or attitude. In animals with microchip implants, the implantation sites were monitored for signs of infection and any abnormal tissue reactions. These animals were also monitored for changes in appetence, behavior and attitude.

California sea lions that were scheduled for procedures involving anesthesia were given a CorTemp ingestible probe within a small fish 1 to 3 hours prior to surgery. Rectal, esophageal and ingestible temperatures were monitored throughout the procedures and were then compared to each other. In addition to the ingestible probes, three California sea lions received implantable Bio-Thermo microchips while under anesthesia. The microchips were placed subcutaneously and intramuscularly under ultrasound guidance in different locations and were compared to rectal, esophageal and ingestible temperatures while under anesthesia.

In bottlenose dolphins, Bio-Thermo microchips were implanted into the subcutaneous space or intramuscularly in different locations under ultrasound guidance following injection of a local anesthetic. The temperatures from the microchip were compared to rectal and esophageal temperatures. CorTemp sensors were fed to the dolphins and temperatures were then compared to rectal, esophageal and/or implantable probe readings until the sensors were either regurgitated or removed endoscopically.

Results

The Bio-Thermo microchip system was found to be a safe method of temperature assessment in California sea lions and bottlenose dolphins. There were no abnormal tissue reactions or infections related to the implantation of the Bio-Thermo microchips. The microchips continue to function to date.

The CorTemp ingestible probe system was found to be a safe method of temperature assessment in California sea lions. All but two of the ingestible CorTemp sensors passed out of the stomach and through the gastrointestinal tract without issue. In these animals, there were no signs of GI discomfort or obstruction during transit through the gastrointestinal tract. Two animals regurgitated the ingestible probes following recovery from anesthesia. It is likely that the regurgitation was related to the anesthesia, and may have occurred regardless of the presence of the ingestible probe.

Conclusions

Both the CorTemp ingestible monitoring system and the Bio-Thermo implantable microchip monitoring system seem to be safe alternative methods of body temperature assessment in California sea lions and bottlenose dolphins. Future investigations will compare these two monitoring systems to each other and to rectal and esophageal temperatures under a variety of working conditions in order to determine their overall efficacy in the marine environment. If found to be both safe and efficacious, these systems would provide the marine mammal community with two mew methods of realtime body temperature assessment.

Acknowledgements

The authors would like to acknowledge the contributions made by the training and animal care staff at the MMP.

The care and use of animals for this project were reviewed and approved by the MMP's Institutional Animal Care and Use Committee (Protocol # 69).