Horse serum is collected from controlled donor herds. It is a cost effective alternative to fetal bovine serum and supports growth of most mammalian cells. However, its usage in insect cell culture is not common. Horse serum has twice the protein content as compared to fetal bovine serum but is low in many trace elements that are required for optimal growth. When using horse serum, supplementing the basal medium with these trace elements can optimize the growth and count of cells. Horse serum also contains certain additional growth factors than other animal sera. For certain hematopoietic cells like myeloid cells only horse serum provides the necessary growth promoting factors. Therefore horse serum is the ideal supplement in nutrient media used for in vitro growth of specific hematopoietic progenitors.