Did you know there’s a specific window of time when a dam can become infected with bovine viral diarrhea virus (BVDV) and can produce a persistently infected (PI) calf? And if the unborn fetus is exposed to the BVDV during the first 120 days of gestation … a calf may be born persistently infected with BVDV.
“If the pregnant cow doesn’t have adequate protection herself, the BVDV can reach the calf fetus,” said Dr. Mark van der List, senior professional services veterinarian at Boehringer Ingelheim. “The immune system of the fetus is developing during this time frame and recognizes the virus as ‘self’ or part of its own body and so doesn’t try to eliminate the virus. These PI animals therefore generate and shed enormous amounts of BVDV, which can infect unprotected herd mates.”
Three steps to reduce PI risk:
The goal is to minimize the possibility of pregnant cows encountering the virus. One of the main sources of virus exposure is from PI cattle that are shedding the virus through bodily secretions every day, all day. PI calves must be identified and removed from the herd. If new animals are being introduced into the herd, confirm they are not PI. Avoid mixing cows together from outside the herd for at least 30 days in case they have a transient infection of BVDV.
2. Removal of PI animals and continuous herd monitoring for new PI animals
Removing PI animals from the herd is key. There are different methods to identify PI animals including ear skin notches, blood samples, and milk samples. Samples can often be pooled and then progressively broken down to find the individually infected animals. Once PI animals are removed, constant monitoring is recommended to detect any new PI animals. The presence of BVDV usually indicates the presence of PI animals. On dairy operations, bulk tank milk can be routinely checked for the presence of BVDV as a monitoring measure. In calves, ear notching at birth is also a good management practice. Your veterinarian can have tissue samples from dead calves and aborted fetuses checked for the presence of BVDV.
Producers should work with their veterinarian to develop a good vaccination program using products that are labeled correctly and backed by solid research. Effective immunization of the herd minimizes the chance of development of PI calves, thus protecting the herd.
Proper vaccine handling is critical to effectively immunize the herd. Make sure the vaccine doesn’t get overheated or exposed to sunlight, and be sure to properly store it in a refrigerator that maintains the desired temperature range. Vaccines should also be administered at the appropriate time to ensure maximum protection during the critical first 120 days of pregnancy. Generally, vaccination right before breeding maximizes the protection against PI calf development.