Specific dynamic effect in the horned frog Ceratophrys cranwelli

Animals exhibit an increase in resting metabolic rate after feeding while they process the ingested food, a response that has been termed the specific dynamic effect. This postprandial rise in metabolism is due in part to the cost of processing absorbed nutrients, especially amino acids, and is particularly pronounced in animals such as large snakes that consume large prey on an infrequent basis. To increase our understanding of the specific dynamic effect in amphibians, we measured the metabolic rates of horned frogs, Ceratophrys cranwelli, before and after they consumed mice or an amino acid solution. After the frogs consumed mice at 20, 25, and 30 C, their oxygen consumption increased within 48 h to a peak that was two- to fivefold greater than the fasting level. The total energy expended depended on the mass of the mice consumed and was not significantly related to variation in frog mass or temperature. Of the energy ingested, 9-15% was expended during the processing of the food. These frogs were as efficient in processing a meal as other vertebrates. After the frogs consumed an amino acid solution, their excess postprandial energy expenditure was less than 25% of the value when they consumed mice of the equivalent amino acid composition. The cost of processing absorbed amino acids cannot be responsible for the majority of the specific dynamic effect in these frogs.