Relationship between digesta transit time and apparent metabolisable energy value of wheat in chickens

1. This study tested the hypotheses that: (a) apparent metabolisable energy (AME) values and whole tract transit time (WTTT) were related, and that (b) the relationship between AME and WTTT differed between male and female Ross broiler chickens. 2. Enzyme products with xylanase activity were added to a basal diet to provide 4 dietary treatments comprising control (no enzyme), Avizyme 1300 (1 kg/tonne), Kemzyme W1 (1 kg/tonne), and Bio-Feed Wheat CT (200 g/tonne). The basal diet comprised (in g/kg), 800 wheat, 155 casein, 20 dicalcium phosphate, 11 limestone, 7 D, L-methionine, 2 vitamin and mineral premix, 3 sodium chloride and 2 choline chloride (60%). 3. AME values for diets were determined in a 7-d energy balance study commencing when chickens were 21 d of age. WTTT was the time elapsed (in min), from time of administration by oral gavage of 200 mg ferric oxide in a gelatine capsule, to time of first observation of the distinctive red colouration in droppings. 4. The mean AME value for the wheat was high (15.7 MJ/kg dry matter) and ranged from 14.4 to 16.3 MJ/kg dry matter for individual birds. Mean WTTT was 206 min and ranged from 105 to 429 min. AME and WTTT were unaffected by enzyme addition to the diet, and the interaction between diet and gender was not significant. 5. There was a significant but weak positive relationship between AME and whole tract transit time, with AME increasing by 2.2 kJ/min. This relationship was unaffected by gender of the chicken.