Methodology to Determine Net Energy in Broilers

The energy cost in broiler diets is likely to continue to increase in the future. Data on heat increment of raw materials used in poultry feed formulations are lacking. An examination of methods to determine net energy is necessary to further develop an accurate net energy assay system. An indirect calorimetry system has been developed at UNE to gather information on respiratory quotient (RQ), heat production, AME and net energy in broilers.

The results of two experiments are described. The first was designed to examine the variation and sensitivity of data collected from indirect calorimetry chambers. Twenty four, 21 d old male broilers (Ross 308) were allocated to 12 closed-circuit chambers. Birds were acclimatised to chambers for four days prior to collecting RQ data and calculation of heat production (HP) using the Brouwer equation from 25 d to 27 d. Apparent metabolisable energy (AME) was determined by total collection of excreta. Birds were fasted for 14 h with fasting HP (FHP) determined on d 28. A second experiment compared AME, HP and NE as measured by indirect calorimetry (IC) or comparative slaughter (CS) in high and low fiber diets. For IC, male broilers (Ross 308; n=32) were used (2 per chamber) to determine AME, HP and NE between 21 d and 24 d as described by Noblet et al. (2010). AME was determined by total collection of excreta. For CS, male broilers (Ross 308; n=240) were used. Birds were slaughtered and analysed at 18 d and 28 d bracketing median growth rate (ADG/BW) of birds in chambers to determine increases in carcass gross energy (GE). Titanium dioxide was used  as an indirect marker to determine AME. After taking diet into account in the model, differences in methods were examined.

Results from the first experiment (Table 1) showed high variation in ADG between chambers but low variation in determination of AME, HP and NE. Based on this variation, it is expected that four replicates would be sufficient to detect an 8% difference in NE between treatments at the 5% level of significance (Aaron and Hays, 2004). In the second experiment, AME, HP and NE as measured by IC vs CS (12.7 vs 12.6 kJ/g feed; 913 vs 887 kJ/kg BW0.70; and 8.82 vs 9.47 kJ/g feed, respectively) were not significantly different (P > 0.05). The results indicate that AME, HP, and NE can be accurately determined by IC. Furthermore, FHP can be determined using the same birds in the IC but not in the CS method.

Aaron DK, Hays VW (2004) J. Anim. Sci. E82:245-254.
Noblet J, Van Milgen J, Dubois S (2010) Proc. Aus. Poult. Sci. Symp. 21, 26-35.