A step-up ractopamine (Paylean) program increases lean tissue in all sexes and decreases fat tissue in boars and immunocastrates

12.2 12.5 11.5 12.3 12.2 12.7 0.20 <.001 0.003 0.15 Lean (%) 69.5 72.8 65.1 67.0 64.4 70.2 2.03 0.006 0.006 0.40 Fat (%) 12.9 8.9 18.9 16.4 20.4 12.3 2.58 0.004 0.004 0.31 Bone (%) 17.1 17.0 16.8 16.7 16.9 16.8 0.18 0.33 0.053 0.97 a SED for Sex x Diet; Dietary RAC increased (P=0.018) lean tissue mass by 4.0, 4.8 and 6.5 kg in the boars, gilts and IM boars, respectively. In the boars and IM boars the increase in lean tissue was accompanied with a decrease (P=0.004) in fat mass, particularly in the latter group. Consistent with previous studies there was little effect of dietary RAC on fat mass in gilts. However, carcass percent fat was decreased (P=0.004) and percent lean increased (P=0.006) in all sexes. Immunocastration caused a decrease in lean tissue mass and an increase in fat mass in response to the absence of male steroids and a dramatic increase in feed intake, particularly over the last half of the study (Rickard-Bell et al., 2005). It appears that unlike for gilts and surgical barrows, dietary RAC may decrease fat mass in entire and IM boars. In conclusion, these data demonstrate that a dietary RAC step-up program can be used to increase lean tissue yields in all sexes and offers an excellent means of minimising the increase in fat mass sometimes observed in IM boars.