About the non-use of MLV vaccines (BVD) on calves nursing cows that had not been vaccinated with a MLV in last 12 months because of the calves shedding the virus. How do the calves shed the virus in order for the cows to pick it up? Is it transferred while the calf is nursing, an exchange of fluids (cow licking calf, etc.), or ? How long is this "shedding" period / how long before a MLV vaccinated weaned calf can be commingled with pregnant cows/heifers that have not had the MLV (only killed) vaccine? Would like to get whole herd on MLV, not sure where/when to start. (Only talking 20 head cows/heifers).