Development and validation of a prediction equation estimating heat production by carbon dioxide entry rate technique.

A series of experiments was conducted to validate the CO2 entry rate technique (CERT) for prediction of heat production (HP) of sheep. Finnsheep cross wethers were used. Carbon dioxide production was estimated by continuous infusion of NaH14CO3 intraperitoneally and collection of saliva. Times required for 14C to equilibrate with the body CO2-bicarbonate pool and excretion of 14C in feces and urine were determined in four wethers (45.5 +/- 1.7 kg) infused for 3 d. Retention of radioactivity was measured for wethers (29.0 +/- 1.9 kg) slaughtered 3 h and 3, 10 and 15 d postinfusion. Using an indirect respiration calorimeter, CO2 production estimates were compared to values derived by CERT for six wethers (45.0 +/- .4 kg) fed at low, medium and high levels of intake. Further data on feed intake level and CO2 production were obtained from 24 wethers in two weight groups (29.5 +/- 1.1 and 42.3 +/- 1.4 kg) fed at three levels of intake. From 12 to 20 h were required for equilibration of NaH14CO3 and the body CO2-bicarbonate pool. Radioactivity of the saliva samples declined rapidly after cessation of infusion. Fecal and urine excretion of 14C was minimal. No detectable 14C was found in tissue of animals slaughtered after CERT. Estimates of daily CO2 production did not differ between the calorimetry and CERT measurements (20.6 vs 20.3 liters/kg body weight .75). Although feed intake levels were different, HP and respiratory quotients (RQ) did not differ between the methods. In the second calorimetry experiment, feed intake level was correlated with estimated HP. Respiratory quotient values did not differ among intake levels.(ABSTRACT TRUNCATED AT 250 WORDS)