Newborn calf serum (or calf serum) can be utilized in cell culture for a few different reasons. If a process is very price sensitive, it makes sense to design using a less expensive product. The newborn calf serum is generally more stable in price and availability compared to FBS if reliability is a key concern. Newborn calf serum is useful in applications where the cell line is robust and cell attachment is the primary goal. Newborn calf serum may not be a good choice where development resources are limited. The culture system will be a little more challenging to design. I do not think I would attempt to substitute newborn calf serum in an existing process utilizing FBS unless there are adequate resources for development. There is a substantial amount of work to be done to verify the system has not been significantly altered by the change.