Colostrum is a mother's milk produced in the mammary glands directly after giving birth.  It contains high levels of protein, immunoglobulins, antimicrobial peptides, and growth factors that strongly enhance the immunity of a newborn.  Research has shown that bovine colostrum, taken in supplement form, has similar effects on the immune system and can increase neutrophil count, promote immunity, help fight infections, and improve gut health.
 
Reference:
Effect of bovine colostrum on the absolute neutrophil counts of Acute Lymphocytic Leukemia patients undergoing Chemotherapy: A double-blind randomized placebo controlled study