Apparent metabolisable energy values of fats for broiler chicks

Seven fats were included at 30, 60 and 90 g/kg (experiment 1) and at 20, 40, 60 g/kg (experiment 2) in a semi-synthetic fat-free diet and in a practical diet respectively. Apparent metabolisable energy (AME) was evaluated with 6 replicate cages each with three Ross 1 cockerel chicks 8 d old. Diets were fed for 11 d and a total collection of excreta undertaken for the last four. There was no significant departure from linearity in the response of dietary AME to added fat, indicating no interactions between basal diet and added fat. In experiment 3 one fat was evaluated at 10 rates of inclusion (10 g/kg to 100 g/kg in 10 g increments) in both a semi-synthetic fat-free basal and a practical basal diet. A significant departure from linearity in the response of dietary AME to added fat was detected but there was no significant fat X basal diet interaction. In experiment 4 twelve commercially available fat blends were each evaluated at 10 rates of inclusion (15 g/kg to 150 g/kg in 15 g increments) in a practical basal diet. Significant departures from linearity in the responses of dietary AME to added fat were observed with some of the fats. It was concluded that the AME of fats mat be determined from multi-level assays by interpolating the quadratic relationships derived.