The effects of age, dietary fat and bile salts, and feeding rate on apparent and true metabolisable energy values in chickens.

1. Apparent (AME) and true (TME) metabolisable energy values of four diets, containing 50 or 150 g animal fat or maize oil/kg, were estimated in young and adult chickens. The diets were given with and without a supplement of 5 g bile salts/kg. Three feeding rates, ad libitum, and 1/6th or 1/3rd of ad libitum were compared. 2. In younger birds, endogenous energy losses were higher when measured in starved birds than when estimated by regression analysis. 3. In young birds, feeding rate had no effect on AME of diets containing 50 g lipids/kg but it significantly affected TME. These results were reversed in adults. AME and TME values of diets containing 150 g lipids/kg were affected by the feeding rate in both young and adult birds. 4. Bile salts increased metabolisable energy values of diets containing high concentrations of saturated fatty acids and their effect was more pronounced in young birds.