At days 18–21, the total amount of excreta per cage replicate was collected and mixed, of which 10% was freeze-dried for
the determination of the coefficient of total tract apparent digestibility (CTTAD) of diet components. Care was taken during
the collection of excreta samples to avoid contamination from feathers and other foreign materials. At day 42, six birds
(male:female, 1:1) per replicate were randomly selected and euthanized by electrocution. A section of ileum was removed
by cutting from the Meckel’s diverticulum to the ileo-caecal junction. A 50ml syringe full of room-temperature deionised
water was inserted into one end of the ileum to carefully flush out the digesta in the gut into a 10 cm diameter Petri-dish
(Liu et al., 2007). The digesta from each replicate were pooled and freeze-dried to calculate the coefficient of ileal apparent
digestibility (CIAD) of diet components.