We compared heat production (HP) and plasma lipid metabolites between meat- and egg-types of Nagoya breed chickens during embryonic development. To investigate HP and respiratory quotient, oxygen consumption and carbon dioxide production were measured using an open-circuit calorimeter system. HP was significantly lower in meat- than in egg-type chickens during embryonic development, and HP gradually decreased with developmental stage in both types. The respiratory quotient was constant at approximately 0.68 at every embryonic stage investigated, and the value was similar in both types. Plasma concentrations of triacylglycerol, nonesterified fatty acid, glycerol and D-3-hydroxybutyrate, which are associated with lipid metabolism, were similar in both types during embryonic development. These results demonstrate that chicken embryos selected for rapid growth of Nagoya breed have characteristic lower HP, and that when selecting chickens for rapid growth, HP is an important parameter during embryonic stages.
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