Everybody using FBS knows the risks of animal derived products. We do not know what is hiding exactly in FBS. We do know that the risk of BSE is considered to be too high in European countries and as low as possible in New Zealand and it’s paramount that it needs to be minimized. 

Using animal derived products like FBS in science means that contaminations or other unwanted substances might be introduced in the process. This calls for reducing risks upfront by using sources that are e.g.. virus free. Currently most trusted is FBS from New Zealand were a relative safe environment exists. The consequence is that this particular version is hardly available in larger quantities.

The risk of contamination with viruses, with prions is a major concern and the alternative with a fully defined, synthetic composition has non of those.