Final answer:
c. Immunotolerance
When an immuno-naive pregnant heifer is exposed to a wild strain of BVD at 120-180 days of gestation, the fetus is likely to develop immunotolerance, meaning it won't mount an immune response against the virus later in life.
Step-by-step explanation:
When an immuno-naive pregnant heifer is exposed to a wild strain of BVD (Bovine Viral Diarrhea virus) at 120-180 days gestation, the likely outcome for the fetus can vary, but in this scenario, the correct answer is c. Immunotolerance. At this stage of gestation, the fetal immune system is capable of recognizing the viral antigens as self, leading to the fetus not developing an effective immune response against the virus later in life. If the BVD infection occurs earlier in gestation, it could lead to embryonic death, congenital abnormalities, or fetal resorption. However, during 120-180 days, the fetus is generally protected from these outcomes, thus the development of immunotolerance is more common.