The killer form of BVD (Pestivirus)

Warrnambool Veterinary recently investigated a beef farm where 17 out of 90 cattle died over a 12 month period due to MUCOSAL DISEASE. The losses started at about 12 months of age and continued intermittently for 12 months. Animals were often found dead, or were sick for 1 to 2 days before death.

Mucosal Disease is a fatal form of BVD which only occurs when cattle persistently infected with BVDV Type 1 become infected with a more virulent strain of BVDV. The disease is usually seen in cattle between 6 and 21 months of age. Mucosal disease causes ulcers in the mouth, intestinal tract, vulva and feet (this can look like foot and mouth disease!), lameness, drooling from the mouth, diarrhoea and death.

When the remaining animals were tested, 13 of the remaining 70 animals were Persistently Infected (PIs). The details of BVD are outlined below. In this case, it almost certain the mothers had never encountered BVD and had no immunity. A Persistently Infected animal was introduced when the cows were pregnant in the first 3 months. A large number of PIs were produced. Why so many apparently normal animals developed secondary Mucosal Disease is still being investigated. BVDV or Mucosal Disease is usually known for causing reproductive losses, abortions, ill-thrifty calves and susceptibility to secondary infections. This is true, but BVD can result in fairly sudden death as occurred in this case

BVDV or Mucosal Disease is usually known for causing reproductive losses, abortions, ill-thrifty calves and susceptibility to secondary infections. This is true, but BVD can result in fairly sudden death as occurred in this case

So, What is BVD?

BVDV is a complicated disease and it is not always easy to understand how it works or what damage it can do on your farm. Bovine pestivirus or Bovine Viral Diarrhoea (BVDV) are the same disease – different people call it different things. We will call it BVDV in this article. BVDV is one of the most complicated cattle diseases we deal with. Don’t worry if you need to ask or read articles a few times to understand the disease. We often do as well.

BVDV can be a serious threat to beef farm production and profitability. This article, some of which comes from the Western Australian Department of Agriculture, explains the effect of BVDV on different groups of animals.

What happens when BVDV occurs?

The effect of BVDV depends on whether it occurs in unborn calves, pregnant cows, feedlot or other cattle.

Unborn calves

Most of the harm done by BVDV is to unborn calves and depends upon timing of infection.

Infection of a naïve cow (one not previously been exposed to or vaccinated for BVDV) in early pregnancy causes loss of the embryo.

Infection of naïve cows in mid-pregnancy can cause abortions, birth defects and live-born calves to be persistently infected with BVDV. These calves spread the disease within and between herds. Most of these calves die within two years of mucosal disease.

By the last third of pregnancy, the calf has developed sufficiently to produce immunity. Some of these calves may be aborted, but most are born healthy.

Pregnant cows

Infection of a naïve cow results in a mild 2–3 week illness that suppresses the cow’s immune system and reduces disease resistance. Most important are the effects on her unborn calf noted above. After recovery these cattle are immune to BVDV.

Feedlot cattle

If a persistently infected animal is introduced to a feedlot, infection will spread to all naive cattle in that pen and adjoining pens within days. It will rarely spread further because usually only persistently infected animals shed an infective dose.

The exposed naïve cattle will develop mild illness and suppressed immunity. As this coincides with transport and social stress, diet change and challenge by other diseases, the health impact of BVDV in affected pens can be significant.

All other cattle

Other cattle exposed to BVDV will also experience a 2–3 week illness followed by lasting immunity. Exposing non-pregnant cattle to persistently infected animals can stimulate immunity and protect future pregnancies in those cattle.

What is Your Risk?

As you can see from the points above, the worst problems with BVDV occur when cattle have no immunity and a carrier animal is introduced early in the joining time. A blood test of 6-10 animals prior to joining allows you to get an idea of the overall status of your cattle.

Of particular interest are the unjoined heifers who have had less chance to develop immunity. Even if there is some BVDV in your herd, there is no guarantee that all animals will be immune.

We advise all producers to blood test 10 or so random animals before joining , especially heifers, to check the immunity level.

What Can I Do?

There is a vaccine available, however, in many cases, simply vaccinating is often not the most cost-effective control measure on your farm.

For the best approach on your farm, talk to a vet at Warrnambool Veterinary.