Estimation of Ileal Endogenous Energy Losses at Different Ages and Influence of Dietary Cellulose Levels in Broiler Chickens

Evaluation of true ileal digestible energy, as a potential energy system for application in broiler feed formulations, requires accurate estimation of the ileal endogenous energy losses (IEEL). The IEEL estimates can be influenced by several factors including bird age and dietary cellulose levels (Khalil et al., 2020). Two experiments were conducted to investigate the influence of age and dietary cellulose levels on the IEEL estimates in (Ross 308) broiler chickens. Titanium dioxide (5.0 g/kg) was added to all experimental diets as an indigestible marker. In experiment 1, a glucose-based purified diet was used to determine the IEEL in male broilers aged 1-7, 8-14, 15-21, 22-28, 29-35 or 36-42 d posthatch. Birds were offered a starter (d 1-21) and/or a finisher (d 21-35) diet before the experimental diet was introduced. The experimental diet was randomly allocated to six replicate cages at each age and, the number of birds per cage was 12 (d 1-7), 10 (d 8-14) and 8 (d 15-42). Ileal digesta samples were collected from the terminal ileum on the last day of each week (d 7, 14, 21, 28, 35 and 42). Diet and digesta samples were analysed for dry matter, gross energy and titanium. The data were analysed as a one-way ANOVA using the General Linear Model procedure of SAS. Bird age had no significant effect (P > 0.05) on IEEL estimates. The IEEL estimates ranged from 1.32 to 1.10 MJ/kg dry matter intake during weeks 1 to 6. In Experiment 2, four glucose-based purified diets were developed using either 0, 25, 50 and 75 g/kg cellulose. In studies with purified diets, cellulose as a structural component is included to texturise the feed. Each diet was randomly allocated to six replicate cages (eight birds per cage), fed from 18 to 21 d posthatch and, ileal digesta were collected on d 21. Diet and digesta samples were analysed for dry matter, gross energy and titanium. The data were analysed as a one-way ANOVA using the General Linear Model procedure of SAS. In addition, the data were subjected to orthogonal polynomial contrasts to study whether responses to increasing cellulose level were of linear or quadratic nature. The IEEL estimates showed a quadratic response (P < 0.05) to increasing cellulose contents. The lowest IEEL (0.37 MJ/kg dry matter intake) was recorded for the diet without cellulose and the highest IEEL (1.80 MJ/kg dry matter intake) observed for the diet with 75 g/kg cellulose. Overall, the present findings confirmed the previous observations in our laboratory (Khalil et al., 2020) that the IEEL in broiler chickens can be quantified using glucose-based purified diets. Bird age has no influence on IEEL estimates in broiler chickens. The dietary cellulose content has a substantial impact on IEEL estimates and the IEEL determined using a purified diet without cellulose represents a better estimate of IEEL.

ACKNOWLEDGEMENTS: We acknowledge AgriFutures Australian Chicken Meat Programme for funding the project.