The 13C 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.