The title may raise questions about definitions of the terms used. The more obvious ones are: 1) What is transfer? 2) How to define toxic; and 3) How to define feed or food. A more underlying question is how to measure the substances we are interested in. The (often) chemical methods used, are not always sensitive or specific enough. Sometimes, biologically based methods are used which detect a biological response, but seldom identify the compound responsible for that. Transfer is often not quantified in absolute terms but expressed in concentrations in feed and food. Mass balance between intake and excretion are quite rare as a steady state situation of residues in the animal is sometimes not obtained. Toxicity is mostly dependent on the concentration of the substance involved and even substances presumed to be innocent. Feed does certainly include the materials provided to the animal but also include the soil in which they walk and graze? Animals will consume some of the soil and it might contain considerable amounts of unwanted substances. Food certainly includes meat, milk and eggs and probably liver and kidney. But does also include intestine, spleen, testicles or even bone? Analytical methods may give wrong results if not applied properly and with adequate background knowledge. The recent episode of melamine in milk powder has been a very tragic wake-up call in this respect. Based on 35 years of carry-over studies with farm animals and data from the literature, a number of these points will be discussed.
carry-over; feed; food; risks; toxic substances; transfer
