Predicting the transfer of contaminants in ruminants by models : potentials and challenges
Certain undesirable substances in feed can transfer into foods of animal origin after ingestion by livestock animals. They become contaminants in food that may threaten the consumers' health. Commonly, feeding trials with animals are conducted to assess the transfer of undesirable substances into animal tissues or milk. Such feeding trials explore the effects on transfer of the various physiological systems (e.g. ruminant and non-ruminant gastro-intestinal tracts) as well as different livestock production intensities. Using alternative methods to mimic the complex physiological processes of several organs is highly challenging. This review proposes a potential cascade of in vitro and ex vivo models to investigate the transfer of contaminants from feed into foods of animal origin. One distinct challenge regarding the models for ruminants is the simulation of the forestomach system, with the rumen as anaerobic fermentation chamber and its epithelial surfaces for absorption. Therefore, emphasis was given to in vitro systems simulating the rumen with its microbial ecosystem as well as ex vivo systems to replicate epithelial absorption. Ruminants contribute significantly to the food sector, not only through meat but also through milk production. The transfer from blood into milk has to be evaluated by employing a suitable model. At the end, in silico approaches are introduced that can fill the gaps or substitute in vitro and ex vivo models. The integratory in silico method of physiologically-based toxicokinetics puts together the information gained from all alternative methods to simulate the transfer of ingested undesirable substances into foods of animal origin.