Proactive steps to prevent persistently infected animals
April 13, 2017
DULUTH, Ga. — A herd infected with bovine viral diarrhea virus via the presence of persistently infected (PI) animals will never be as productive as it could be. BVDV exposure can drag down performance in cattle herds not only by reducing milk production and reproductive efficiency, but also by suppressing herd immunity and making animals more susceptible to other diseases. A three-part approach to controlling BVDV can help prevent and eliminate persistently infected (PI) animals in the herd.
There's a specific window of time when the dam can become infected with BVDV and can produce a persistently infected (PI) calf. 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."
Steps to Reduce PI Risk
“If the pregnant cow doesn’t have adequate protection herself, the BVDV can reach the calf fetus. 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.” Dr. Mark van der List, senior professional services veterinarian at Boehringer Ingelheim
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Biosecurity: Biosecurity is a critical step in preventing PI calves. 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.
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.
"The spread of BVDV ultimately depends on the underlying immunity of the herd," said Dr. van der List. "If the herd has zero protection, then it can spread very rapidly. However, if a good vaccine and biosecurity program are in place, PI animals have been removed and the herd is being monitored, there will be minimal risk of BVDV."
Vaccination: 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 also should 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.
Work with your veterinarians to develop a comprehensive BVDV control plan to that will protect your herd. F