High Plains Journal, KS
03-09-07
BVD prevention can increase profits
"Some of the worst reproductive losses related to BVD that I have been involved
with have occurred after salebarn calves have been allowed to mingle with
pregnant cows," said Dr. Terry Engelken.
By Jennifer Bremer
There has been a lot of time, energy and research devoted to looking at Bovine
Viral Diarrhea virus, but researchers have learned more about it in the last five
years to be able to help deal with the health problem.
Dr. Terry Engelken, associate professor of veterinary diagnostics and
production animal medicine at Iowa State University's College of Veterinary
Medicine told attendees at the Cornbelt Cow-Calf Conference the BVD virus is
responsible for many different clinical signs in cow-calf and stocker operations.
"It can affect the reproductive tract, the brain, the digestive system and can make
respiratory disease more severe. This virus can work directly on the different
body systems or it can cause secondary disease due to the fact that it
suppresses the animal's immune system," he said.
BVD can lead to open cows, calf scours, respiratory diseases and lower gains
according to Engelken.
Many times the BVD infections are not noticed in older animals because they
don't appear to be ill. However, BVD can cause fetal loss at any stage of
gestation, will make respiratory and intestinal disease outbreaks worse and can
cause death.
Infection can be short or long term
BVD can be in a herd through an acute or routine infection when the animal
comes in contact with the virus within the field. Clinical signs are usually mild or
nonexistent, but animals may have a fever, lower feed intake, mild diarrhea, and
lowered milk production.
Engelken said the main consequences of acute infections is the horizontal
spread of the virus to herd mates.
"The primary way in which BVD survives in your cow herd is through the
production of persistently infected (PI) animals. These PI animals serve as
carriers and remain infected for life," he explained.
PI animals constantly spread the virus to other animals through the urine, feces,
blood, saliva and discharges from their eyes and nose. PI animals are produced
when the virus infects the pregnant female and then reaches the developing
fetus prior to day 125 of gestation.
"This period is before the immune system of the fetus is able to recognize the
virus as a foreign invader so it fails to mount and immune response against it," he
said.
It is estimated that 0.25 to 1.5 percent of all calves born are born as PIs. These
calves may be aborted, born weak or appear normal, but they continuously shed
the virus from their body secretions. The problem rises when the normal
appearing animals join the replacement pool and continue to expose the herd
with the virus.
Engelken said getting the proper diagnosis and setting up a prevention plan is
critical to topping these continued losses, regardless of the type of enterprise.
Harboring the PI animals, especially in a cow-calf operation is very important. He
said that these animals need to be eliminated from the herd in order to prevent
the spread of the disease.
Test to prevent spread
Testing should begin in either the suckling calves and/or the replacement
animals. The calves are important because the PI animals in this group are
guaranteed to expose the pregnant females during the subsequent breeding
season and produce more PI animals.
The replacement animals that need tested would include open and pregnant
heifers and bulls that are intended to be used in a breeding program.
Testing for the virus can be done in different ways and Engelken suggested
consulting the herd veterinarian to determine the best option.
"It is fairly easy and cheap to test your animals for this virus and can make a
huge difference in production," he said.
Preventing BVD infection include understanding the risk of BVD introduction,
timely vaccination and the testing of new additions to the herd. Since BVD is
spread by animal to animal contact, the risk will increase if new animals are
introduced to the herd or brought to the farm.
He suggested isolating new animals for at least 30 days before letting them
mingle with the rest of the herd.
"If you have a stocker or feedlot enterprise in addition to your cow herd, it is
imperative that you prevent nose-to-nose contact between these two sets of
cattle at all times," he said. "Some of the worst reproductive losses related to
BVD that I have been involved with have occurred after salebarn calves have
been allowed to mingle with pregnant cows."
Vaccinate to prevent spread
He admitted there is no single answer or recipe for vaccinating, but vaccinating is
a must. Different animals can be at different levels of exposure or risk of
infection. The vaccine should always have fetal protection to help prevent the
birth of PI animals. He suggested using modified live vaccines when the animals
are open because they tend to work better than the killed vaccines.
"The goal is to not have BVD in your herd, but there are many biosecurity issues
that need to be followed to have total prevention," said Engelken. "Ideally closing
a herd is the best way to prevent BVD, but that isn't always possible, so
screening all animals that enter the herd is a must and know the origin of the
herd and health program before letting those animals on your farm."
BVD continues to cause problems regardless of the enterprise or size of the
cattle operation. He said eliminating the problem requires an understanding of
how the disease develops and maintains itself in the herd.
Engelken said the best way to deal with a disease like BVD is to put together a
cost effective program to protect your investment.
Jennifer Bremer can be reached by phone at 641-938-2342 or by e-mail at
jbremermaj@hotmail.com.