As we already that Probiotics help to maintain normal gut microflora. Bovine colostrum like human colostrum has anti-infective factors, and helps to prevent infection.
Colostrum contains several compounds like macrophages, immunoglobulins, several proteins that have antimicrobial as well as immuno stimulatory effects. So along with probiotics, such factors from colostrum must be mediating immuno modulation in gastrointestinal system.