The apparent metabolisable energy (AME) values for selected samples of wheat, barley, triticale, oats and sorghum grown in Australia were determined in energy balance experiments with young broilers of both sexes. Ileal digestible energy values were measured for most of these samples. Inherent characteristics of grains induced different responses in male and female chickens. Results indicated that the metabolic activity of gut microflora influenced the energy values in a sex-dependent manner. This has very important implications for the nutrition and husbandry of commercial broiler flocks. It may become economically worthwhile to feed and manage broilers in single sex flocks rather than jointly, as is the current situation. In conclusion, sex-related differences may be important in the uptake and utilisation of energy and other nutrients, in response to anti-nutritional factors (including non-starch polysaccharided; NSP), feed enzymes, prebiotics, probiotics, and other feed additives, and in vaccinations against gut pathogens.