Milk or colostrum may serve as the source of MAP organisms
for neonates in 2 ways. Fecal contamination of these fluids
may occur, allowing the milk or colostrum to act as the vehicle
for infection. Additionally, MAP has been isolated from sterile
collections of milk and colostrum from infected cows (30),
indicating that there is potential for direct transmission through
colostrum and milk from an infected dam (31). Infection can
also occur directly across the placenta, as tissue-positive fetuses
have been found in culled tissue-positive cows, although this
occurrence is quite infrequent (32). This happens more often
in cows displaying advanced clinical signs of JD; however, it can
occur in cows that are heavy fecal shedders, yet not displaying
clinical signs of disease (33).