BOVINE VIRAL DIARRHOEA VIRUS

(BVDV)or ‘Pestivirus’

Michael Healy

Outline of presentation:

• What is BVDV? What does it do?

• Economic impacts of a BVDV outbreak on a South Coast dairy herd

• Effects of BVDV on beef cattle producers

• Some recommendations for control

What is Bovine Viral Diarrhoea Virus?

• Also known as ‘Pestivirus’• A contagious infection of cattle• When a beast is infected, it

develops an immune response, recovers, and is then protected against re-infection for the rest of its life. So why worry???

Reproductive losses!

• BVDV causes reproductive losses when previously unexposed (naïve) breeding females are infected

• The ‘danger time’ for infection is around the time of mating/insemination or during the first 6 months of pregnancy

What sort of reproductive losses?

• Infection around the time of mating:–Conception failure–Abortion of early embryo– Increase in returns to service

The ‘danger time’

What sort of reproductive losses?

• Infection during first 6 months of pregnancy:

– The virus crosses the placenta and infects the foetus

– Aborted foetuses

– Stillbirths– ‘Dummy’ calves – born with brain or eye

abnormalities– Birth of PI calves

What’s a PI calf?

• “Persistently infected” with BVDV

• Produced when a naïve heifer/cow is infected between 30 and 125 days pregnancy, and the foetus survives

• The PI calf will be a carrier of BVDV for life

• The PI animal is a “virus factory”

• PI animals spread the virus to other cattle they come into close contact with

• Most PIs are “poor doers” – they grow slower than other calves/weaners and are often sick

• Unfortunately, some PIs will appear normal and healthy

CASE STUDY: BVDV in a Bega Valley dairy herd

• 950 cows in milking herd

• Year-round calving

• Calf-rearing unit and heifer property are separate property to dairy

• Pregnant cows are sometimes bought-in

ABORTION STORM!

•Since August, 2008:

- 30 mid-term abortions

- 25 early abortions (pregnant, returned to service)

- Overall herd conception rate reduced by 10%

15% of heifer calves are PIs!25 heifer calves have been ‘dummy’ calvesAbout 5 premature looking calves with patchy baldness

75 heifer calves have died or been destroyed!

Losses

• Normal calves reared alongside PIs

• High rate of respiratory infections and scours in the non-PI calves

• Slow growth rates

Calf hutches

• Reduced income from selling surplus springer heifers ($1500 each)

• Reduced milk production (heifers replacing cows)

• Veterinary bills

• Labour costs

• Lost contracts to rear Wagyu calves

• Reduced ability to voluntarily cull cows

Other losses…

Over $150,000!

Where did the PI come from?

• In an introduced pregnant cow (a “Trojan cow”) withPI calf

•Other possibilities:- Introduced PI cow- PI bull- Access to PI across boundary fence

Beef cattle

• Aborted foetuses, stillbirths

• Poor pregnancy rates

• Extended calving period

• Low weaning rates

• Poor weaner growth rates

• Stunted calves

• Dummy calves

• Sick calves – pneumonia, scours

BVDV in a beef herd:

- Be very careful!

- Yarding animals together at ‘danger time’

- Conception failure

Synchronised AI and embryo transfer breeding

programs

Economic impacts on beef herds:

• Naïve herd:- decreased weaning rate

- decreased weaner growth rates

- abortions, stillbirths, dummy calves and PI calves

- PIs can grow up normally and infect breeding females, causing further reproductive losses in 3 years

- Decreased income for 13 years!

- $42 loss per female per year for 13 years

Economic impacts on beef herds:

• Previously exposed herd:- Some heifers (~30%) were naïve

- The rest were protected by lifelong immunity

- The impact was smaller

- $30 loss per female per year for several years

1. Don’t let your cows or heifers get infected with the virus for the first time when they are being joined or during pregnancy.

2. Controlling PI animals is the key to controlling disease!

BVDV2 key points:

• PACE test – to detect PI

animals. About $10 per animal

tested. Can be done by owner.

•AGID test (a blood test):

– detects Pestivirus antibodies in the blood. About $12 per animal tested.

- can test a sample of heifers or cows from a larger group, to see how many have been exposed to the virus before

Diagnostic tests

• A vaccine is available – “Pestigard”

• 81% effective

• Protection requires 2 shots in the first year, and 1 shot every year after that

• Cost per shot is about $6

Pestivirus Vaccine

What can you do to protect your herd against

BVDV?There are a few options:

- Vaccination

- Partial vaccination

- Autovaccination

- Removal of PI animals

- Biosecurity measures

Vaccination

• For hobby farmers and farmers with a small herd, this may be the easiest thing to do.

• Share bottles of vaccine with neighbours

• Vaccinate animals twice in first year

• Once each year after that

• Vaccinate heifers, cows and bulls

Partial vaccination• Vaccinate only some groups of animals, e.g. replacement heifers and bulls

• Vaccinate animals most at risk (have never been infected)

• AGID blood test (for Pestivirus antibody) on a sample of animals from each group

• Vaccinate those groups that have a high proportion of animals with no antibodies

Autovaccination

• The PI animal is deliberately used to expose your animals to BVDV

• You must confirm that the animal being used is really a PI (by PACE test)

• Expose females to PI several months before joining

Removal of PI animals

• May be a good option in small, closed herds

• $10 per head to screen whole herd

• Might get expensive in large herds

BIOSECURITY!• This means keeping PIs from other farms away from your stock

• Biosecurity is very important

• Other control options (e.g. vaccination, removing PIs) MUST be combined with good biosecurity

What are some good biosecurity measures??

• Keep a closed herd

• Make sure introduced animals are not PIs, including bulls (PACE test)

• Don’t mix groups of cattle during the ‘danger time’

• Avoid introducing pregnant females

• Avoid over-the-fence contact with neighbouring cattle

• Transporting cattle to shows, agistment

Summary of key points:

• BVDV a.k.a. Pestivirus – common, costly

• PIs are the source of infection

• Don’t let your females get exposed for the first time at mating or during pregnancy

• Biosecurity

• Vaccination