Ask the Expert: Dr. Neil Michael

Q1: Should I test calves for BVD PI status?
BVD remains one of the most costly diseases in the U.S. cattle industry and is responsible for more than $2 billion in losses each year. Despite great advances in vaccine technology, BVD remains in dairy populations primarily through persistently infected (PI) animals as a result of BVD exposure of the dam during the first trimester (40-120 days) of pregnancy.

A high percentage of PI animals die within the first six months, but a small percentage that live often appear normal and cannot be detected visually. When comingling your calf herd, PI calves shed BVD virus to herdmates through saliva, urine and feces, resulting in higher treatment (scours/pneumonia) costs and increased overall death rates. At breeding age, BVD negatively impacts fertility and results in elevated pregnancy loss.

Therefore, a routine screening program for BVD PI animals is the only way to ensure that you currently or in the future do not experience these losses in your calf, breeding and lactating herds.

Q2: How do I implement a BVD testing program for my calves?
All calves, DOA and late-term abortions should be tested at birth by taking either an ear notch or blood sample to submit for PI testing. Positive animals should be removed from the premises and euthanized immediately.

Next, implement proper screening tests the lactating adult herd. The dams of PI calves should be tested for PI status since all PI cows will have PI calves.

Screening calves is only part of a complete herd BVD control program that includes an effective vaccination program for all ages, routine screening of bulk tank milk and testing of all incoming herd replacements animals (including bulls).

Q3: What else should I know about BVD PI animals?

• Just because all PI animals are apparently eliminated, new PI animals can be produced by pregnant animals exposed to circulating BVD within the herd from non-PI animals. Therefore, constant testing is critical for long term control of BVD.
• Vaccination programs alone do not eliminate the risk of PI animals; proper screening is necessary to ensure that BVD PI animals are not causing hidden losses in your calf operation.
• PI animals may appear “normal” even though they are shedding millions of BVD virus particles into their environment and exposing herdmates.