The effects of endogenous energy, type of diet, and addition of bile salts on true metabolizable energy values in young chicks.

A trial was carried out using 3-week-old chickens of a commercial breed to study the effects of either a fat-free diet or a diet containing 150 g/kg of animal fat on the endogenous energy losses measured with starved birds. The effects of the addition of different levels of bile salts to such diets and the accuracy of true metabolizable energy (TME) with respect to the other modes of expression of metabolizable energy were also examined. The excreted endogenous energy values were shown to vary not only according to the type of diet (P less than .01) but also in relation to the dietary intake level (P less than .01). Because it is directly related to endogenous energy, TME proved to be an inaccurate parameter in young chicks unless values were corrected for N-balance. If the values of both apparent metabolizable energy (AME) and TME are corrected for N-balance, they are normally comparable and independent of the dietary intake level if the diet contains virtually no added fat. These findings indicate that most of the endogenous excreta are composed of nitrogenous metabolites. However, neither AME nor TME values of fat-rich diets are independent of dietary intake. The addition of bile salts had no effect on the metabolizable energy values of the fat-free diet. However, in the case of the diet rich in saturated fats, they compensated either for insufficient bile secretion or for endogenous bile salts degraded by the intestinal microflora. Thus, the digestive utilization of dietary fat, especially that of the saturated fatty acids, palmitic and stearic acids, was increased. In addition, metabolizable energy was significantly improved (P less than .01) by the addition of bile salts when the dietary intake level increased to the ad libitum level.

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.