Advice of the Scientific Committee of the Belgian Food Safety Agency regarding the presence of endogenous anabolics and or prohibited substances in food producing animals

The following questions were asked to the Scientific Committee on the presence of 
endogenous anabolic and/or prohibited substances in food-producing animals: 
- Question 1: Among the substances being examined by the FASFC, which are those 
whose presence in a matrix of animal origin is suspected to have an endogenous 
origin (metabolism, feed, ...)? 
- Question 2: In which matrices and in which animal species (categories), the presence 
of substances of endogenous origin can be observed? 
o Can a residue concentration be determined differentiating an endogenous origin 
from an illegal treatment for combinations substance/matrix/species? 
- Question 3: Can the presence of prednisolone and thiouracil in matrices other than 
urine also have an endogenous origin? 
o If this is the case, can a residue concentration be determined which can 
differentiate the origin (endogenous versus illegal treatment) for combinations of 
substance/matrix/species?