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Respiration chambers share one analyzer working in parallel, and methane (CH4) concentrations have to be measured at certain intervals. The maximum and minimum values in the kinetics of CH4 emissions can be missed during the interval between measurements, which may influence the quantification of CH4 emissions. Chambers must be opened for morning feeding and cleaning, which causes a loss of CH4 data. Calculation methods are needed to estimate the lost CH4 emission data, which may influence the estimated amount of daily CH4 emissions. In this study, we measured the CH4 emissions of 10 growing Chinese Holstein dairy heifers in respiration chambers. Methane concentrations were measured every 0.5 min to obtain the 23-h kinetics of CH4 emissions, which were further selected at different intervals between measurements (i.e., 5, 30, 60, 120, 180, and 240 min) to evaluate the effects of interval on quantification of CH4 emissions. The missing 1-h kinetics of CH4 emissions before feeding were not measured, and 2 calculation methods were used to estimate the missing 1-h kinetics of CH4 emissions: mean value of measuring period (the mean method) and the nearest value of measurement just before chamber opening (the nearest method). The results showed that the rates of CH4 emission from 10 heifers varied from 4.56 to 11.42 g/h. The increment of intervals decreased maximum rate of CH4 emission and increased minimum rate of CH4 emission. Interval caused less than 5% of the difference in measuring CH4 emissions. Although the mean method had greater estimated daily CH4 emission than the nearest method, the difference was within 3%. The interval between measurements (≤3 h) and calculation method had little influence on enteric CH4 emission measurements.

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OBJECTIVE: The net energy requirement for the maintenance (NEm) of broilers was determined using regression models by the indirect calorimetry method (ICM) or the comparative slaughter method (CSM). METHODS: A 2×4 factorial arrangement of treatments including the evaluation method (ICM or CSM) and feed intake (25%, 50%, 75%, or 100% of ad libitum recommended) was employed in this experiment. In the ICM, 96 male Arbor Acres (AA) birds aged d 15 were used with 4 birds per replicate and 6 replicates in each treatment. In the CSM, 116 male AA birds aged d 15 were used. Among these 116 birds, 20 were selected as for initial data and 96 were assigned to 4 treatments with 6 replicate cages and 4 birds each. The linear regression between retained energy (RE) and metabolizable energy intake (MEI) or the logarithmic regression between heat production (HP) and MEI were used to calculate the metabolizable or net energy requirement for maintenance (MEm) or NEm, respectively. RESULTS: The evaluation method did not detect any differences in the metabolizable energy (ME), net energy (NE), and NE:ME of diet, and in the MEI, HP, and RE of broilers. The MEI, HP, and RE of broilers decreased (p<0.01) as the feed intake decreased. No evaluation method× feed intake interaction was observed on these parameters. The MEm and NEm estimated from the linear relationship were 594 and 386 kJ/kg of body weight (BW)0.75/d in the ICM, and 618 and 404 kJ/kg of BW0.75/d in the CSM, respectively. The MEm and NEm estimated by logarithmic regression were 607 and 448 kJ/kg of BW0.75/d in the ICM, and were 619 and 462 kJ/kg of BW0.75/d in the CSM, respectively. CONCLUSION: The NEm values obtained in this study provide references for estimating the NE values of broiler diets.