RACTOPAMINE RESIDUE LIMITS. “In the USA, ractopamine is allowed to be used at a feed concentration of 5–20 mg/kg feed for finishing pigs and in dosages of 5–10 mg/kg feed for finishing pigs heavier than 109 kg. In Canada, ractopamine is allowed in meal or pellet feed for finishing barrows, gilts, beef cattle and heavy turkeys only. The maximum residues limit of ractopamine is 50 and 10 ppb in the USA and Japan, respectively.”
http://en.m.wikipedia.org/wiki/Ractopamine