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Variation in the response of multiple genetic populations of pigs to ractopamine

Animal Sciences Department, Purdue University, West Lafayette, IN 47907-1151

¹ Correspondence: E-mail: aschinck{at}purdue.edu.

Abstract

Several research trials have evaluated the impact of ractopamine on barrows and gilts of various genetic populations. Overall, the desirable response of ractopamine to increase daily carcass lean gain, improve feed efficiency, and increase carcass lean percentage has been observed in genetic populations of substantially different lean growth rates and carcass lean percentages. Six trials have evaluated the magnitude of genetic populations x ractopamine interactions. In one trial, carcass muscle accretion (g/d) increased with ractopamine to a greater extent in high-lean-gain (High-Lean) barrows than in low-lean-gain (Low-Lean) barrows (P < 0.02). Dissected fat accretion (g/d) was reduced by a greater magnitude in the High-Lean than in the Low-Lean barrows (P < 0.04). A second trial evaluated the ractopamine response in five genetic populations of barrows and found significant ractopamine x genetic populations interactions (P < 0.05) for daily carcass lean gain. Regression of the carcass lean gain of pigs fed ractopamine on the mean carcass lean gain of the controls for the five genetic populations indicated that the ractopamine effects could be described as a constant percentage (25%) increase in daily lean gain above the controls. The third trial evaluated the response of Paylean in 300 gilts in a 3 x 4 factorial with three genetic populations (commercial terminal crosses) and four ractopamine levels (0, 5, 10, and 20 ppm). The genetic populations had similar carcass lean percentage. No genetic populations x ractopamine interactions were found (P > 0.10). Overall, the research indicates that ractopamine has a positive impact on barrows and gilts with substantially different genetic potentials for lean growth and carcass lean percentage. The ractopamine response to increase lean growth has been found to be proportional to the genetic potential of the genetic populations. Recent research has found significant genetic populations x environmental interactions for pigs reared in different health status environments. Environment x ractopamine and environment x ractopamine x genetic populations interactions for compositional growth in pigs need to be evaluated.