By: Dr. Michelle Arnold, DVM- Ruminant Extension Veterinarian (UKVDL), University of Kentucky
There is mounting
concern in KY regarding the identification and subsequent movement of “BVD-PI”
animals into livestock sales. The BVD
virus is primarily believed to cause immunosuppression and contribute to
substantial respiratory disease and death loss in the stocker/backgrounder
sector. Unfortunately, with increased
awareness and use of a simple, inexpensive diagnostic test to identify PI
animals, the question of what to do with a positive calf must be addressed. Adding to the dilemma is the unprecedented
price of calves in the markets today - it is not an exaggeration to say that a
$1000 steer can become essentially worthless due to the positive result of a $3
test. Often the reaction to a positive
test in a newly purchased calf is to sell the test positive animal as quickly
as possible in a livestock auction - much like getting rid of a “hot potato”-
to keep from spreading BVD to other calves on the farm and to minimize
financial loss. The problem is if these
PI calves are purchased a second time and end up causing or contributing to a
large respiratory outbreak with high morbidity (sickness) and mortality
(death), who is at fault? The State
Veterinarian has deemed it necessary to stop the “dumping” of positive calves
on the market to the best of his ability and authority. To that end, KY laboratories must report
positive test results to the Office of the State Veterinarian (OSV). Upon receiving those results, the OSV will:
1. Contact
the owner/attending veterinarian regarding the current status and location of
the animal.
2. Provide
an opportunity for the owner to understand the impact of the disease and the
laws governing the State Veterinarian’s response.
3. Present
options to the owner for managing the cattle involved:
a) Isolate
and retest in 2-3 weeks to confirm the diagnosis.
b) Transport
to slaughter with OSV permit.
c) Isolate
either on owner’s farm or at permitted feedlot and feed to slaughter only.
d) Euthanize
and dispose of by an approved method.
Test positive animal
is not to be sold, given away, or transported without approval of the State Vet.
Given the
importance of this issue, it is essential to understand what a “PI” truly is
and how one is found. The problem begins
on the farm of the cow/calf producer or heifer developer. If a pregnant cow or heifer is infected with
the BVD virus between 42-125 days of gestation, her unborn calf contracts the
virus and is never able to get rid of it for the rest of its life. When this calf is born, it is “persistently
infected” or a “PI” calf and can be considered a “carrier” of the virus for the
duration of its lifetime.
The “PI” animals
are the reason BVD disease continues.
They are the primary source of virus transmission because they shed an
extremely high number of virus particles throughout their lives. A PI animal is a virus factory, producing
millions of virus particles in all body secretions including feces, urine,
saliva, nasal discharge, milk, semen, uterine secretions, and aborted
membranes. These contaminated body fluids
are deposited on the grass, in ponds, watering troughs, feed troughs-virtually
everywhere the animal goes. Although it
is often assumed that PI calves are stunted, will grow poorly and usually die
young, some are absolutely normal and will survive well into adulthood and have
calves. Unfortunately, if a PI female
gets pregnant her offspring will be a PI calf 100% of the time. This is important because if one
PI calf is out in the pasture constantly shedding virus during breeding season,
many (if not all) of the cows will be exposed during the highest risk
time. This is especially true of
seasonal breeding because contact with a single PI calf can infect a large
proportion of cows in the first trimester.
In reality, the
virus is much more of a problem at the cow/calf level than the stocker/backgrounder
level. To answer the question if BVDV is
circulating in the herd, a producer must be aware of what is going on within
his herd and keep accurate records to determine if at high or low risk. Ask yourself this series of questions:
1. Does my herd have poor reproductive
performance (high infertility) despite good nutrition and fertile bulls (if AI
is not practiced)?
a. Is there a decrease in overall pregnancy
rate and % pregnant after the first service?
b. Are there more abortions, stillbirths,
neonatal deaths, and weak calves than usual?
c. Are cows returning to heat more often
than expected?
2. Do I see any physical abnormalities
(dummy calves, eye defects, cleft palate) in the calves at birth?
3. Do
I have unexplained suckling (baby) calf loss due to pneumonia or scours?
4. Do I introduce new cattle (including
bulls) into the herd without testing for BVD?
5. Do feeder calves or the neighbor’s herd
come in contact (fence line) with my lactating herd?
6. Is there a significant population of wild
animals (such as deer) on my farm?
7. Have I neglected to vaccinate my cattle
against BVD?
If you answered
“yes” to any of these questions, your herd is at risk for BVD (the more “yes”
answers, the higher the risk). Your goal
should be to know with certainty if the virus is in your herd and, if found,
work to eliminate it. If you answered
“no” to all of the questions, your herd is at low risk for BVD so your goal is
to keep the herd free of the virus and stop it if it is introduced. In either case, the tools of diagnostic
testing, vaccination, and biosecurity will all be needed to
accomplish your individual herd goal.
Diagnostic
testing for BVDV is important for two distinct reasons. The first reason is to find out if the virus
is causing a clinical disease problem in your herd. Sending any aborted fetuses and membranes,
stillbirths and/or dead calves to a laboratory will help to confirm the
presence of the virus. The second and
perhaps most important reason to test is to identify any PI cattle in order to
remove or isolate them before they spread the virus and infect other
cattle. Recall that PI (persistently
infected) calves result when a cow is infected with the BVD virus between
42-125 days of gestation or if a PI cow has a calf. Once the calf is born, it sheds millions of
virus particles in all of its body secretions throughout its life. Therefore it is crucial to get these PI
animals away from any cows/heifers in the first trimester of pregnancy and stop
the creation of new PI calves. The most
commonly used sample for identifying PI cattle is skin, usually taken as an ear
notch. Blood (serum) can also be used
but not in young stock (calves less than 3 months old). If you suspect BVD virus is in your herd and
you want to initiate testing, remember to:
1. Test calves early preferably before
placing the bull in a breeding group if possible in order to remove PI calves
from cows/heifers in the early stages of pregnancy
2. Test all calves and, if positive, isolate
and retest in 3 weeks to confirm the result; if (+) then euthanize the calf and
test the dam. Remove (+) dams either by
slaughter (with OSV permit) or euthanasia.
3. Test any open cow if her calf died or was
sold untested. Slaughter positives.
4. Test all bulls and replacement heifers
(purchased or raised). Slaughter positives.
5. For Pregnant cows-test calf when it is
born. If calf is positive, retest to
confirm; euthanize calf if (+) then test cow.
6. Quarantine and test all purchased
pregnant cows and, if negative, they can join the herd. However, bear in mind
her calf could still be a PI so, when her calf is born, test her calf and, if
positive, isolate the cow/calf pair and retest calf to confirm; then euthanize
calf if (+).
7. Any BVD ELISA positive test result (at
the UKVDL) should be confirmed by segregating the animal and retesting ear
notch or blood drawn at least 3 weeks after the first sample. True PI animals will still be positive after
3 weeks. Other laboratories may have
different protocols so check with your veterinarian or laboratory on the need
for confirmatory testing. Remember PIs are considered defective and
there is a moral and ethical obligation to dispose of these animals without
returning them to commerce.
To aid in the
control of BVDV, effective vaccines are available to combine with management
practices in order to prevent/limit its introduction into the herd. For heifers and open cows, modified-live
vaccines should be given 4-6 weeks prior to breeding season to reduce the risk
of reproductive problems and fetal infection.
The herd should receive at minimum an annual vaccination with at least
5-way viral protection and Leptospirosis.
Calves should be vaccinated after 4 months of age; ideally with 2 doses
of a modified-live vaccine given at least 2 weeks apart (observe label warnings
regarding nursing calves or consult your veterinarian). Consult your veterinarian for specific
recommendations for your herd. Other
important management practices to reduce the risk of BVDV include:
1. Screen newly purchased cattle for the
presence of the virus (submit ear notch or serum) and isolate until the results
are known. Remember that pregnant cows
may be test negative for BVDV but the unborn fetus may be PI so you must test
the cow and her newborn calf.
2. Show cattle should be isolated 3-4 weeks
after returning to the farm.
3. Test new bulls before they are used
(virus can live in the semen).
4. Prevent potentially BVDV contaminated
objects (boots/vehicles/equipment) from entering the premise.
5. Limit wildlife interaction with the cows
if possible.
6. Vaccinate the herd annually with modified
live vaccine to maintain immunity in the event of exposure. If using killed vaccine, precisely follow
label directions regarding boosters.
7. Manage pastures to minimize fence line
contact with other cattle, especially during early pregnancy.
Consult with
your local veterinarian on the best way to detect BVDV on your farm as well as
to assess the most biologically appropriate and cost-effective control
measures. Successful control will result
in improved productivity, reproductive performance, health, and ultimately
economic return. Removal of PI calves while on the farm will reduce sickness
and death for stocker/backgrounder operations and remove the need for
regulatory action at the state level. The
only way a good control program will work within our state is for all of us to
be on board and willing to work out a solution.
Decisions must be made on how to fund BVD elimination programs as well
as how to best carry them out but it is well within our ability if it becomes a
priority.
