The C bicarbonate dilution technique to determine energy expenditure in young bulls validated by indirect calorimetry

We explored the applicability of the ¹³C bicarbonate dilution technique for determination of energy expenditure (EE) in young bulls in comparison to whole body indirect calorimetry (IC). Twelve bulls of a F2 German Holstein x Charolais cross (4.5 months, 332 ± 16 kg BM) received a diet providing 1000 kJ ME d^? 1 kg BM^? 0.75 and 4.3 g crude protein d^? 1 kg BM^? 0.75. Bulls were housed in respiration chambers and received an intravenous bolus of NaH¹³CO₃ (A: 3 μmol kg BM^? 1 (n = 2), B: 7 μmol kg BM^? 1 (n = 4), C: 17.5 μmol kg BM^? 1 (n = 6), 99 at.% ¹³C) into the jugular vein to measure EE. Simultaneously, EE was determined by IC. After the ¹³C administration blood samples and breath gas were collected from the animals in the respiration chamber during a 24-h period (7.00–7.00 h). The recovery of ¹³C in breath CO₂ (% of ¹³C dose) was irrespective of NaH¹³CO₃ dose (A: 69.7 ± 2.7%, B: 70.5 ± 4.5%, C: 75.0 ± 4.9%; P > 0.05). Only small amounts of ¹³C were excreted in urine (3.4 ± 2.6%) and feces (2.0 ± 1.3%). The EE determined by the ¹³C bicarbonate method using breath and blood ¹³C recovery rates as correction factors was not different from that measured by IC (816 ± 81 blood] or 827 ± 101 breath] vs. 820 ± 90 kJ d^? 1 kg BM^? 0.75). Bland–Altman analysis showed a 95% confidence interval for EE of ± 99 and ± 109 kJ d^? 1 kg BM^? 0.75 based on blood and breath ¹³C recovery, respectively. In conclusion, the ¹³C bicarbonate dilution method is appropriate to obtain reliable estimates of EE in young bulls using blood CO₂ or breath CO₂ under standardized experimental conditions, i.e. in the fasting state.