EFFECT OF COLD-ACCLIMATION ON OXIDATIVE CAPACITY AND RESPIRATORY PROPERTIES OF LIVER AND MUSCLE MITOCHONDRIA IN DUCKLINGS, CAIRINA-MOSCHATA

1. The effect of cold acclimation on the oxidative capacity of the ske letal muscle (gastrocnemius and pectoralis) and the liver of ducklings was investigated. 2. In cold-acchmated (CA) ducklings, the oxidative capacity of the liver was higher (+40%) than in ducklings reared at th ermoneutrality (TN). In these animals an increase in state 4 respirati on and a decrease in the respiratory control index (RCl) was also foun d. 3. The oxidative capacity of both pectoralis and gastrocnemius musc les also increased in CA animals. 4. In these muscles the oxidative ca pacity of the subsarcolemmal mitochondrial fraction of CA ducklings wa s higher (+96% in the gastrocnemius and +58% in the pectoralis) than t he intermyofibrillar one (+51% in the gastrocnemius and +33% in the pe ctoralis). No variations were observed in either the RCl or the ADP/0 ratios. 5. These findings indicate that the energy expenditure needed for non-shivering thermogenesis (NST) in cold-acclimated ducklings can be met by the increase in the oxidative capacity of the skeletal musc le and the liver, each by different mechanisms; the gastrocnemius musc le would seem to play a prominent role.