Are you guys sure that there is no evidence for these levels of metabolites of either this, or of Clen, arising from the ingestion of commercially-available meats?
If you read the USADA's statement on Wilson and its zeranol web page, you'll see USADA does not mention any studies showing these hormones make it into the food supply. Plus they point out that, as a matter of fact, positive tests are very rare among both animals or athletes.
This should not be a surprise. These hormones are delivered via implants, which are injected into animals at a fairly young age. The hormones then leak out until they are basically used up. Given this set up, it's hard to see how an animal could end up with excess levels of the hormones.
When these implants were first developed, manufacturers had to show they didn't leave residue. This led to a spate of studies looking at blood and tissue levels of the hormones after the implantation. Those studies all showed hormone levels below FDA/USDA standards before the usual slaughter age.
If you want to read the underlying studies, just google some combination of "the hormone name"+ residue + food + studies.
PS There is a twist. Some of the by-products of a fungus that infects feed can be metabolized into zeranol in a cow's stomach. So maybe...