Body size and metabolic rate in the laboratory rat

When the basal metabolic rates of living beings from different species are compared, a relationship between metabolic rate (M) and body size (S) can be identified as follows: M = a Sb, where b is close to 3/4. The present study investigated whether the same relationship applies within a species. In the laboratory rat, Rattus norvegicus, it was found that b can vary considerably from one sample of animals to another. The value of b was also affected by the activity level of the animals, but not by moderate cold exposure. The best estimate for the basal intraspecific b in the rat may be closer to 2/3 than to 3/4, but the variability of the experimental data prevent a definite conclusion at this point. Further research is necessary to explain the variability between different samples of rats.