A negative BVD antigen test means it is very unlikely that individual is a Persistently Infected (PI) animal. It could still pick up BVD virus and become transiently infected with BVD virus at any point during its life including at markets and at livestock shows. If it is pregnant at the time of infection this can lead to a ‘Trojan PI’ – that is the calf from a purchased animal may be a PI when it is born and spread the virus to other cattle on your farm. The best advice is to isolate any cattle moving on to your farm for 3-4 weeks. Test any calves born to cows moved on to your farm is promptly at birth eg tag and test.