Growth performance of Hubbard x Cobb 500 and Ross x Ross 708 male broilers fed diets varying in apparent metabolizable energy from 14 to 28 days of age

The cost of energy-contributing ingredients has increased over the last several years. Defining minimum dietary energy specifications for broilers is a strategy to mitigate high diet cost. Two experiments were conducted to evaluate the effects of diets with graded concentrations of AME<inf>n</inf> fed to Hubbard × Cobb 500 (experiment 1) and Ross × Ross 708 (experiment 2) male broiler chicks from 14 to 28 d of age. Both experiments were identical in experimental procedures with the exception of genetic strain. Broilers were fed a common corn-soybean meal-based starter diet from 1 to 13 d of age. At 14 d of age, dietary treatments were provided with 1 of 6 concentrations of AME<inf>n</inf> (3,000, 3,030, 3,060, 3,090, 3,120, and 3,150 kcal/kg). In experiment 1, BW gain, feed intake, and FCR of Hubbard × Cobb 500 broilers decreased linearly with increasing AME<inf>n</inf>. Linear broken-line response of FCR was estimated at 3,062 kcal of AME<inf>n</inf>/kg based on broken-line methodology. In experiment 2, Ross × Ross 708 broilers did not respond to graded concentrations of energy, as indicated by linear and quadratic regression of BW gain, feed intake, caloric conversion, and FCR data. Therefore, Hubbard × Cobb 500 male broilers respond to AME<inf>n</inf> from 14 to 28 d of age and may be fed diets formulated at 3,062 kcal of AME<inf>n</inf>/kg without loss of performance. Conversely, growth performance of Ross × Ross 708 male broilers was not affected by varying AME<inf>n</inf> (3,000 to 3,150 kcal/kg) from 14 to 28 d of age. In addition, the response to AME<inf>n</inf> may not be as pronounced with the modern broiler compared with broilers used in previous research.