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If cows and heifers become infected within the first 120 days of gestation, the unborn calf may become persistently infected or PI. A calf will only become PI if its mother is infected during pregnancy; it cannot become PI after birth.
PIs will shed high quantities of BVD virus into their environment for life. They are the most significant source of infection to other cattle.
Within infected herds, PIs often only account for 1 or 2 out of every 100 animals. It is contact with these PI animals that leads to infection of other animals within your herd, causing the signs listed above.
Please note that the BVDFree Scheme is not in a position to advise farmers on their specific BVD control plans. These should be discussed with a vet.