Effects of Intermittent Ractopamine Hydrochloride Use on Pig Growth Performance in Late Finishing1

Two experiments were conducted to evaluate the effects of feeding, withdrawal, and refeeding 10 ppm ractopamine hydrochloride (RAC) on pig performance. In Exp. 1, the 4 treatments consisted of 1) a control diet fed for 56 d before marketing; 2) RAC fed for the first 21 d, and then the control diet fed for the last 35 d; 3) RAC fed for the first 21 d, the control diet fed for 14 d, and then RAC fed for the last 21 d; and 4) the control diet fed for the first 35 d, and then RAC fed for the last 21 d. Pigs fed RAC for the last 21 d of the study or those fed RAC from d 0 to 21 and then from d 35 to 56 had greater (P < 0.01) ADG and G:F than control pigs. In Exp. 2, the 5 treatments consisted of 1) a control diet fed for 56 d; 2) RAC fed for 56 d; 3) RAC fed for the first 21 d, the control diet for fed for 14 d, and then RAC fed for the last 21 d; 4) the control diet fed for the first 7 d, RAC fed for 21 d, the control diet fed for 7 d, and then RAC fed for the last 21 d; and 5) the control diet fed for the first 35 d, and then RAC fed for the last 21 d. When RAC was fed for 21 d and then withdrawn for either 7 or 14 d and refed for 21 d, the pigs had the same overall ADG and G:F as those fed RAC for only the last 21 d of the study.