Researchers in cell biology are familiar with adding bovine or calf serum to cell cultures. Serum a supplement containing growth factors required for cell growth. Unfortunately, adding serum means adding a highly variable non-standardized product to a well ordered system. The non-standard origin of the serum requires extensive testing of serum batches to find the batch compatible with your cell types.
Cell culturing with serum means working with a product of animal origin, essentially a waste product of an abattoir. Culturing under stringent conditions is not the primary interest of the abattoir. The price of the serum tends to be a reflection of the level of care each facility takes with its quality control. Prices are an effect of serum demand and the relative health of the animals used to obtain the serum. Recent developments show a continuous price increase which might be caused by shortage.