Broiler response to diet energy

Male broiler chickens were fed corn-soybean diets providing 2,700, 2,900, 3,100 or 3,300 kcal ME/kg. In all experiments, each treatment was tested with three replicate groups of 30 birds grown to 49 d of age. In Experiment 1, birds consumed the various diets ad libitum whereas in Experiment 2, all birds received identical and restricted quantities of feed so as to ensure variable intakes of energy. In a third experiment, after 7 d of age, broilers had access to feed in two feeders that contained only the highest level of energy, or the 3,300 kcal ME/kg diet in combination with one of the other diets previously described. Providing diets of 2,700 to 3,300 kcal ME/kg for ad libitum consumption had no effect on growth rate (P > 0.05) and energy intake was constant; however, reducing the energy level of the diet did result in reduced carcass fatness (P < 0.01). When feed intake was controlled in Experiment 2, there was reduced growth (P < 0.01) rate as energy level of the diet was reduced. This reduced growth was associated with dramatic reduction in carcass fatness (P < 0.01), although breast meat yield was not affected. When broilers were offered a choice of diets, they showed remarkably precise control of intake, such that energy intake was again constant across all treatments. However, even though energy intake was constant, broilers consuming the choice diets involving the lower energy content diets tended to have less carcass fat. It is concluded that the broiler still possesses a good ability to control its feed intake based on desire to normalize energy intake. As energy intake is decreased, or there is increased protein intake, the bird deposits less carcass fat.