The impact of feeding carbadox from 12 to 75 pounds bodyweight on the rate, efficiency, and composition of growth in pigs with a high and low genetic capacity for lean tissue growth (LG) was evaluated. The high LG pigs gained bodyweight and muscle tissue faster and utilized feed more efficiently than low LG pigs. High LG pigs also had carcasses with more dissectible muscle and less dissectible fat. The pigs’ responses to carbadox feeding were dependent on the LG genotype. Feeding carbadox from 13 to 75 pounds bodyweight resulted in improved body growth and efficiency of feed utilization, but the magnitude of the responses were greater in the high LG pigs. Dietary carbadox additions from 13 to 75 pounds also resulted in greater muscle growth rates and carcass muscle content at 75 and 250 pounds in the high but not the low LG genotypes. Based on these data, the value of dietary agents such as carbadox that control or destroy antigens in the body need to be based on the impact of the agent on carcass composition as well as rate and efficiency of body growth. Furthermore, the value of the agent will be increased as pigs’ genetic capacity for lean tissue growth is increased.