Adapted from Western Australia Department of Agriculture 

Bovine pestivirus or Bovine Viral Diarrhoea (BVDV) are the same disease – different people call the 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 notpreviously 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.

Table 1 What immunity status definitions mean

NaiveNever infected
Cattle that have never been infected or challenged by BVDV.
They have no antibodies to the virus.
ImmuneHave been infected but are not carriers
Cattle that have been infected with BVDV but are not carriers.
They have antibodies and are immune to future infections.
There are two ways this immunity can occur:
• infection as BVDV circulates through the herd – immunity is lifelong (‘natural immunity’)
• vaccination – annual boosters needed to maintain immunity.
Persistently InfectedCarriers
Carriers of BVDV secrete the virus for their entire life.
They exhibit variable signs and degree of disease and most die 1–2 years after birth.
The calf of a persistently infected heifer or cow will also be persistently infected. Persistently infected bulls are also potent spreaders of BVDV.

 

Table 2 Effect of BVDV infection on cattle according to pregnancy status

Non-pregnant naive cattle2–3 week infection
short-term immune suppression
lifelong immunity to BVDV following infection
Pregnant naive cattle1–4 months gestation
2–3 week infection
embryo death, abortions, stillbirths, mummified foetuses
any live calves are persistently infected
4–5 months gestation
2–3 week infection
abortions, viable or non-viable calves delivered at full term
congenital deformities and defects
some calves born normal and immune to BVDV
5–9 months gestation until birth
2–3 week infection
abortions
any calves born alive at full term immune to BVDV

Table 3 Signs of BVDV

Poor fertility 
low calving rates
high rate of pregnancy tested not in calf cows (PTNIC)
Reproductive abnormalities
abortions
stillbirths
mummified foetuses
congenital deformities and defects
calves that die soon after birth
Outbreaks of disease
fever
not wanting to eat
dullness
lethargy
recovery usually takes a few days.
pneumonia, scours or other diseases, particularly if other stress factors are present. Production losses can be high.