The contribution of growth to the SDA response in pythons

The specific dynamic action (SDA) of food represents the postprandial increase in metabolic rate and has often been described as the cost of digestion. However, many recent studies suggests that the SDA response primarily reflects the energetic cost of growth. Here, we estimated the contribution of growth to SDA in juvenile Burmese pythons (Python bivittatus) through simultaneous measurements of oxygen consumption (V̇O2) and growth over 50-56 days with snakes being fed at different intervals to generate variation in growth. The linear relationship between SDA (=∫(V̇O2-SMR); where SMR is standard metabolic rate) and growth was used to estimate the energetic cost of growth. This estimate was then multiplied by total growth to quantify the contribution of growth to the SDA response. Protein retention was assessed from faecal nitrogen, and changes in body composition were quantified using CT scans. Growth accounted for approximately 77% of the SDA response. The estimated contribution to the SDA response was supported by high protein retention and proportional increases in lean tissue. Together, these results strongly indicate that SDA in Burmese pythons is dominated by growth-related processes, particularly protein synthesis.