Heat production and respiratory enzymes in normal and runt newborn piglets

The heat productions of newborn runt and normal piglets were estimated over a range of ambient temperatures. Most runts increased their heat production in the cold, but when expressed as J X kg-0.67 X min-1 it was significantly lower than in normal piglets (201.3 +/- 16.0 and 144.7 +/- 16.2 J X kg-0.67 X min-1 for controls and runts, respectively, at 32 degrees C). Runts consequently had lower deep body temperatures (37.8 +/- 0.2 and 36.8 +/- 0.3 degrees C for controls and runts, respectively, at 32 degrees C). Some runts failed to increase their metabolic rate in the cold and these had the lowest deep body temperature. Activities of respiratory enzymes in heart and diaphragm muscle were similar in all animals, whereas the longissimus dorsi of runts had significantly lower enzyme activities (76.3 +/- 4.2 and 55.5 +/- 6.6 in absorbance units for controls and runts, respectively).