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Two experiments were conducted to determine the influence of sire line and dietary energy levels on grow-finish pig performance. In each experiment, dietary treatments were corn-soybean meal based diets with no added fat and corn-soybean meal based diets with fat added and soybean meal adjusted to maintain a similar lysine: calorie ratio. Fat additions to the added fat diets ranged from 3.75% for the 40 to 70 pound body weight period to 1.5% for pigs over 220 pounds body weight. Within each of five phases during the growing-finishing period, feed budgets were used to maintain a similar total caloric intake between experimental diets. In both experiments, pigs were progeny of Danbred NA 230 females. In Exp. 1, the sire lines compared were Danbred NA 771 versus Danbred NA 671. In Exp. 2, the sire lines compared were Danbred NA 771 versus Danbred NA 600. There were no interactions between sire line and dietary treatment in either experiment. There was no effect of dietary treatment on daily gain. In Exp. 1, feed conversion was improved 6.8% and in Exp. 2, feed conversion was improved 3.7% for the fat added diets versus the control treatment. The lack of daily gain response, when combined with the lack of a genetic interaction, suggests that for these genetic lines daily gain is not a consideration in the decision regarding the use of fat in grow-finish diets.