One of the dairy industry’s nagging quandaries has been ridding herds of bovine viral diarrhea (BVD). The virus was first discovered in 1946 and has been found on every continent except cattleless Antarctica.
BVD can cause decreased reproduction, lower feed efficiency, higher mortality and morbidity rates. Exposure to persistently infected (PI) cattle is costly.
Adding up the cost is a daunting task, says Derrell Peel, Extension livestock marketing specialist at Oklahoma State University. “BVD impacts all sectors of the industry [but] in different ways,” he says. “An awful lot of the loss is probably not even recognized by producers.”
An array of economic studies in the U.S. suggests the following losses:
Peel estimates the total loss to the cattle industry, both beef and dairy, is a staggering $1.54-2.59 billion. He cautions estimates vary widely because of different population sets, methodologies and economic assumptions.
“I think these numbers probably capture the impacts in a general sense across the industry,” Peel says. “I think the important part is that it’s a big number.”
BVD is a ribonucleic acid (RNA) virus, which means it can mutate and change rapidly. “This rapid mutation can lead to diverse clinical signs,” says Dan Grooms, DVM, professor at Michigan State University’s College of Veterinary Medicine. “It is not just diarrhea.”
The hallmark of BVD is immunosuppression, which leads to problems like respiratory disease.
A BVD-persistently infected (BVD-PI) animal occurs when a pregnant cow comes into contact with another BVD carrier infecting the fetus. The infection can then lead to a variety of reproductive outcomes: abortions, congenital defects, early embryonic deaths or even live BVD-PI calves.
It is rare for families of BVD-PI cattle to exist, so a producer would seldom see a PI-calf born from a PI-cow. However, Grooms notes that PI-cattle have lived for as long as eight years at Michigan State.
BVD-PI calves are immunosuppressed, typically poor performers that die at an early age and infect other cattle during their short life.
“As long as the PI-animals are alive, they will be shedders of the virus serving as a reservoir of infection to animals they come in contact with,” Grooms says.
BVD is spread to healthy cattle via nose-to-nose contact or other exchanges of bodily fluid such as milk, semen, feces, urine and saliva.
To control BVD, there are three important steps in the prevention chain:
- Implementing biosecurity by reducing the risk of the virus entering a herd through contact with PI-cattle.
- Identifying and eliminating PI-cattle from herds to stop disease transmission.
- Improving herd immunity via vaccine immunization
None of these approaches will work on their own, Grooms says. But when used together, they will go a long way toward protecting cattle and the dairy supply chain. The ultimate goal is to eliminate BVD losses all together.
Executing the plan
It is hard to find a case of BVD on Milk Unlimited Dairy Farms near Atlantic, Iowa. Their managing partner Kelly Cunningham aims to keep it that way.
Cunningham says the keys to success on any dairy are controlling costs and improving performance.
The 3,400-cow dairy produces five tanker loads of milk per day. This March, the Iowa farm yielded its best milk results with cows averaging 86 lb.
A slowdown in production due to BVD and any related respiratory issues would be costly, so BVD-PI testing has been part of the management program since 2010. “We want healthy cows because they tend to milk more than the ones having problems,” Cunningham says.
All heifer calves on his farm have an ear notch taken within two days of birth and tissue samples are sent to a lab for a pool testing protocol. Testing with a pool of 20 animals has helped significantly reduce the cost for Milk Unlimited Dairy Farms.
Pooling costs $2 per animal to pool. However, should a PI-positive pop up in the pool test, it costs $5 individually to retest. “That’s not a lot of money in my mind,” he says compared to the risk of spreading BVD.
Baby calves that are found positive for BVD-PI are then euthanized immediately.
Some outside springers have been purchased in the past to help increase the herd size, and those animals are tested on arrival. Purchased springers that test BVD-PI are sent straight to a cull plant for slaughter.
“If we do buy cattle from outside of our farm, we try to get them directly from the grower or producer,” Cunningham says. He doesn’t want to buy heifers that are from put together groups, running a greater likelihood of exposure to infected cattle.
Thus far, 9,586 calves and 3,075 springers have been tested. Two purchased springers have tested PI-positive since testing began back in October 2010. Six baby calves have tested PI-positive, and the last two have originated from BVD exposed purchased springers.
“We are working toward a closed herd with the use of sexed semen and better pregnancy rates, and we have been able to generate a lot more heifers,” Cunningham says.
In addition, cows are vaccinated to prevent both BVD Type 1 and 2 at prebreeding, generally at 35 days in milk. Calves are vaccinated at 35 days of age and receive a booster shot 28 days later.
Calves are individually housed in hutches for 70 days to limit nose-to-nose contact. Feed buckets and manure buckets are kept separate on the loaders to reduce cross contamination.
Heifers move onto a development facility where they get another booster. At their second pregnancy check (approximately 90 days pregnant), an additional vaccination is given.
“We believe that herd health and the calf program have gotten better because of these steps,” Cunningham says. “We also believe this is the right thing to do.”
Bringing the lab to the farm
Despite starting in 2012, Daisy Farms outside Paris, Texas ranks toward the top in the region for size, milking 1,000 cows and farming 7,600 acres. The farm supplies milk to produce Daisy brand sour cream and cottage cheese.
In the fall of 2014 the incidence of pneumonia and scours was starting to rise in calves. Older cattle were also exhibiting some respiratory symptoms and abortions were occurring at a higher rate.
As a veterinary pathologist, Richard Kerr took a deeper look at what was occurring via a microscope. He serves as the manager for Daisy Farms’ research and diagnostics labs.
Kerr says at first glance the histopathology of the samples indicated there was severe chronic bacterial pneumonia occurring with cultures showing the bacteria Staphylococcus sciuri. More samples were taken showing bacteria such as Aerococcus viridans, Proteus mirabilis and Kocuria kristinae.
“We started to notice a pattern with the types of bacteria we were identifying,” Kerr says. Almost all of the bacteria were associated with immune system compromise. It pointed to something more at play, possibly a viral infection, he adds.
Tests for viral respiratory diseases like Bovine Syncytial Respiratory Virus (BSRV), Infectious Bovine Rhinotracheitis (IBR) and Parainf luenza 3 (PI3) were administered. Only one positive case came back for BSRV.
However, a serology test pointed to a 1% incidence of BVD in the herd.
“It left us at a crossroads because serology tells us there is BVD somewhere. It doesn’t tell us if there are PIs or what we are dealing with,” Kerr says.
This led Daisy Farms down the road to testing with real time-PCR tests on farm. After working with an equipment company to speed up the testing process, Kerr’s lab can examine 768 samples in an 8 hour shift.
All animals in the herd are tested at these particular times:
- Suspect calves in the first few days of age
- Purchased animals prior to shipping and quarantine on arrival
- Purchased animals on arrival; release on double negative results
- Test 10% or 10 animals on movement across farm facilities
- Test all animals 21 days prior to expected calving date
In November 2014 there were three positives for BVD-PI. Since then there has been one positive case in both July and August 2016 confirmed using realtime PCR. The cattle were then removed from the herd.
Kerr views the BVD protocols as a larger disease prevention and health promotion strategy. “We don’t just use this workflow for BVD, we use it for a variety of testing scenarios,” Kerr says.
In addition to testing for BVD, Daisy Farms also looks for Leptospira borgpetersenii, Blue Tongue Virus, Anaplasma spp. and Bovine Leukemia Virus.
However, the most successful testing procedure has been for mastitis, Kerr says because the lab can use the speed of real time-PCR to select the correct antibiotic for quick treatment. This has increased antibiotic efficacy from 69% to 97%.
Following the BVD issue, there were still scours problems on Daisy Farms, and Bovine Coronavirus was identified as a culprit. The dairy started vaccinating their herd for Coronavirus in early March and scours occurrences have since dropped by 80%.