Have edited (although all the information i can find talks about boldenone Undecylenate being derived from Testosterone), but this paragraph from the same is important and should not be ignored:
http://www.losalamitos.com/pdfs/chrb/CHRBAdvisories.pdf
The CHRB’s anabolic steroid regulations are modified from the RMTC model rules,
which in turn are based on long established international regulations for anabolic steroids.
Testosterone, nandrolone, and boldenone are endogenous anabolic steroids. Endogenous means
they occur naturally. The normal levels of these endogenous anabolic steroids have been well
established in the horses for urine and the regulatory threshold levels for a violation have a wide
safety margin. Horses that have not been administered anabolic steroids are not in danger of a
positive. However, boldenone is manufactured as Equipoise®; nandrolone is manufactured as
Durabolin®; and testosterone is manufactured as generic testosterone.