Using Ultrasound to Measure Muscle and Blubber Thickness as a Metric for Body Condition in Tursiops truncatus
Abstract
Body condition and weight are frequently utilized as indicators of health in veterinary patients.1 Among marine mammals in managed care, subtle changes in weight can be difficult to detect without access to a scale, and external signs are often obscured until the animal has sustained significant weight loss.2
Ultrasound has been utilized for decades to measure subcutaneous and visceral adipose tissue, as well as the thickness of other body tissues (e.g., muscle).3 Blubber is a specialized, subdermal adipose tissue found in most marine mammals that acts as a thermal insulator and a source of metabolic energy, while also contributing to improved buoyancy and hydrodynamics. The thickness, quality, and composition of blubber varies across ontogeny and among life history stages, as well as in response to thermal and nutritional challenges.3,4,5
Body blubber index (BBI) was recently utilized to establish the “ideal” body condition in Tursiops truncatus.6 However, obtaining measures of both blubber and muscle thickness is optimal, as muscle wasting is an indicator of illness and injury that can contribute to weight loss.1 Efforts to systematically validate these measures with other nutritional and health related markers are limited. As such, BBI, blubber thickness (cm), and muscle thickness (cm) were compared to girth (cm), estimated weight (kg)7, BMI, and water temperature (°C) utilizing a population of 10 subadult and adult Tursiops truncatus (nmales=7, nfemales=3) housed at Dolphins Plus and Dolphins Plus Marine Mammal Responder in Key Largo, FL. Morphometric values, coupled with muscle and blubber thickness measurements (using ultrasound), were obtained and recorded monthly for 7 months. Ambient water temperature ranged from 13.61–35.89°C (56.5–96.6°F) during the study period.
BBI, blubber thickness, and muscle thickness were all positively correlated with girth, estimated weight, and BMI (p<0.001). Additionally, BBI and blubber thickness were negatively correlated with water temperature (p<0.001). Neither muscle thickness nor weight exhibited a significant relationship with water temperature.
These preliminary results suggest that BBI, blubber thickness, and muscle thickness are valid indicators of body condition and nutritional state in bottlenose dolphins, supporting the clinical utility of ultrasound measurements in managed care.
Acknowledgements
The authors wish to thank Dolphins Plus and Dolphins Plus Marine Mammal Responder, Key Largo, in particular Richard Borguss, Art Cooper, Nancy Cooper, Katie Hernandez, and the Training staff for access to the dolphins, training procedures, and enabling extensive data collection. In addition, the authors would like to thank SeaWorld for enabling data collection for three of the animals participating in the study.
* Presenting author
+ Student presenter
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