Diets with an increasing amount of co-products and formulated with a constant or declining net energy (NE) content were compared for ATTD of gross energy and for nitrogen retention. Forty gilts 38.5±1.2 kg BW were individually allocated and fed ad libitum with the experimental diets for a 69d period. Fecal and urine samples were collected two times for growing and for finishing periods. ATTD decreased when co-products were added, even when NE content held constant. Nitrogen retention was lower when co-products were added to the diet. In conclusion diets containing up to 36% co-products and formulated using NE resulted in poorer NR than a corn-soybean meal control diet. Formulating to a constant NE did not maintain nitrogen retention.