Introduction

The use of electrical conductivity of a subject as an indirect method of assessing body composition has been made for many years, particularly in the field of biomedicine (for reviews see Van Loan, 1990; Kushner, 1992; Yanovski et al., 1996). The technique employed primarily by biomedics is known as bioelectrical impedance analysis (BIA: Chapter 6), in which the electrical conductivity of the subject is measured between discrete points on the subject's surface.

BIA differs from total body electrical conductivity (TOBEC®) measurement, because, in the latter, the whole subject is placed within a chamber surrounded by a conductive coil, producing a measure of total body conductivity. The acronym TOBEC has been registered as a trademark of the main manufacturer (EM-SCAN). In theory, greater standardization can be achieved using TOBEC® than with BIA as the need to attach electrodes to the skin surface, which might cause problems in most non-human animals, is removed. The TOBEC® method of determining body composition does not cause discomfort to the subject, is relatively rapid and requires little special training to use (Fiorotto et al., 1987). It has been used on a wide range of animals including fish (Bai et al., 1994; Gillooly & Baylis, 1999), reptiles (Angilletta, 1999), birds, e.g. Scott et al. (1994, 1995) including birds' eggs (Williams et al., 1997) and mammals, e.g. Gosselin & Cabanac (1996), Raffel et al. (1996) including humans, e.g. Presta et. al. (1983), Van Loan et al. (1987), Kretsch et al. (1997).