FBS for stem cells - standard and ES-qualified Fetal Bovine Serum (Aug/08/2009 )

Is there anyone here who works with non-ES cell-qualified FBS? Is there any significant difference between the standard qualified and the ES cell-qualified serum? I know that the price differences are considerable, but I wonder if it's just it.
Any help, please?

I have cultured murine es cells on mef feeder layers using both es cell qualified and regular fbs. Qualified serum is tested for factors known to induce differentiation or alter proliferation of es cells. otherwise, it is just regular serum. Since it is so much more expensive, we have, on occassion, used regular fbs. I saw no difference in amount of spontaneous differentiation/death/growth than with the qualified stuff. But, that just means that the lot used must not have had any negative factors. It can be like rolling a dice, so you may not want to order a lot of regular fbs with the same lot in case one lot doesn't work for you.