NAVLE Nuggets: Bovine Abortions (pt 2)

Case number one.

Let's start with a herd that has a reproductive problem.

A producer reports increased early embryonic death, infertility, abortions, weak calves, and some calves born with neurologic abnormalities including cerebellar hypoplasia.

The herd has also recently had evidence of BVDV exposure.

What should you be thinking? Your top differential should be bovine viral diarrhea virus.

BVDV is one of the most important viral causes of reproductive disease in cattle.

And here's the key.

The outcome depends heavily on when the fetus becomes infected.

This is one of these topics where knowing the gestational timeline can really make a NAVLI question much easier to answer.

So let's talk a little bit about that.

If a cow is infected with BVDV during gestation, before 40 days of pregnancy, infection can result in infertility and embryonic death.

So think early infection, pregnancy doesn't establish or doesn't continue.

If a cow is infected with BVDV between 40 and 125 days of gestation, this results in a persistently infected calf.

If the fetus survives infection during this period, it may become persistently infected, and these calves are immunotolerant to the virus and can shed large amounts of BVDV throughout their lives.

That makes PI animals extremely important sources of infection within a herd.

So, a PI calf equals an infection with BVDV which occurred before the fetal immune system could recognize BVDV as foreign.

Now, if a cow is infected between 100 and 150 days of gestation, this can cause congenital abnormalities, particularly in the CNS.

Potential abnormalities include cerebellar hypoplasia, hydrocephalus, hydroencephaly, microcephaly, and spinal cord hypoplasia.

Ocular abnormalities can also occur, including cataracts, retinal degeneration, and micro-ophthalmia.

So if you see a calf with cerebellar hypoplasia, which is a classic sign, BVDV should immediately be on your list.

And finally, if a cow is infected with BVDV after 125 days...

This can result in abortion or clearance of the virus.

The fetus is increasingly capable of mounting an immune response.

So they may clear the virus, but sometimes it can cause abortion.

So how do we diagnose BBDV? Diagnosis can include PCR, virus isolation, immunohistochemistry via ear notch testing, which detects persistently infected calves, or detection of pre-cholesterol antibodies.