5.3. Cold acclimation and nonshivering thermogenesis (III)

Three-week cold acclimation resulted in less changes in ducklings than in quails. In ducklings, no clear changes in the metabolism occured in vivo during cold exposure, nor in measurements of cytochrome c oxidase activity in muscles in vitro. The most prominent induced changes were increased body weight, increased leg temperature in cold and a decrease in relative weights of liver and leg muscles. In the quail, cold acclimation induced changes in the metabolic rate (higher oxygen consumption in cold, a shift in the LCT from 23.8°C to 21.1°C, a lower shivering threshold temperature in m. pectoralis and higher respiration in vitro) and morphometric changes including an increase in body mass, relative weights of heart and intestine, and a decline in the water percentage of the m. gastrocnemius.

Cold-acclimated Japanese quail chicks and Pekin ducklings lacked clearly distinguishable NST. The amplitude of the shivering EMGs paralleled the increasing oxygen consumption in at least one of the muscles studied. In ducklings, the amplitudes of shivering were low (<30V) both in the control and cold acclimated groups. In both species, the highest shivering amplitudes were recorded from cold-acclimated birds.