Precolostral screening of newborn calves for the detection of BVDV in

large dairy herds

Jeremy Schefers, DVM

Minnesota Veterinary Diagnostic Laboratory

Herds with 500+ cows represent 50% of the total dairy cows on 4.5% of all farms

Screening herds for BVDV

• Serology (acute and convalescent, SN titers)

– Confounded by widespread use of vaccine

• Sentinel calves (non-vaccinated calves)

– Multiple groups needed on large farms

• Bulk milk RT-PCR– Only detects lactating PI and lactating PIs are rare

• “PI hunting”

Bovine gestation and fetal infection

with non-cytopathic BVDVConception

Day 80

Day 120

Day 80-120 Gestation:

Development of BVDV PI calf.

Birth Day 280

Day ~120 – term:

These calves have BVDV antibodies at birth and prior to colostrum feeding. “Precolostral serum antibodies”

Conception to 80 days: fetal loss

PI SeroconversionEED

•EED

Day 80

Day 120 Day 280

PI Seroconversion

Day 0

PI versus fetal seroconversionDiagnosing a PI (a rare event) • Assume prevalence = 0.5%.

Sample size:– 90% confidence 459 animals– 95% confidence 597 animals

Seropositive calves are five to ten times more common than PI’s.

• Assume prevalence = 5%. Sample size:

– 90% confidence 44 animals– 95% confidence 58 animals

EED

Precolostral sampling - Compliance

Precolostral samplingHerd Calves

sampledNo. (%)

antibody +No. (%)

RT-PCR +PI (%)

CA 236 19 (8.1) 4 (1.8) 2 (0.9)

CA 210 14 (6.7) 3 (1.4) 0 (0)

MN 226 12 (5.3) 2 (0.9) 1 (0.4)

MN 289 20 (6.9) 16 (5.5) 5 (1.7)

Total 961 65 (6.8) 25 (2.6) 8 (0.8)

Precolostral screening• Advantages

– Detects fetal infections in both pregnant cows and heifers

– Relatively economical

• Disadvantages– Detects a historical infection– May be confounded by MLV vaccines given to

pregnant cattle during the last two trimesters

Serological evaluation of precolostral serum samples to detect bovine viral

diarrhea virus infections in large commercial dairy herds

Accepted for publication in JVDI, September 2008

Jeremy Schefers, Claudia Munoz-Zanzi, James E. Collins, Sagar M. Goyal, Trevor R. Ames

Chapter 3: Detection, characterization and control in a large dairy herd

Herd Calves sampled

No. (%) antibody +

No. (%) RT-PCR +

PI (%)

CA 236 19 (8.1) 4 (1.8) 2 (0.9)

CA 210 14 (6.7) 3 (1.4) 0 (0)

MN 226 12 (5.3) 2 (0.9) 1 (0.4)

MN 289 20 (6.9) 16 (5.5) 5 (1.7)

Total 961 64 (6.8) 25 (2.6) 8 (0.8)

480 cows

480 cows

Maternity Fresh cow

Far-off dry cows

Close-up dry cows

Heifers

Parlor

500 lactating dairy cows

Direct contact with another 500+

New introductions are common

Biosecurity protocols are uncommon

Herd health• Post-partum metritis and pneumonia

approached 30-40%.• Episodes did not correlate with predictable

changes and were described as being sporadic.• Poor treatment response• Economic impact = $80,000 per year

– $64 per calving

BVD CI and metritis rate

0%

5%

10%

15%

20%

25%

30%

35%

40%

February May August November

month

Per

cent

cow

s .

metritis

CI rate

Challenges• Should we test all animals for BVDV PI?• How many PI cattle will have to be removed?• What will this cost? (estimate $20,000)• Are the PI test accurate?• How can you determine that all PIs were

detected?• Can all test results be explained?• Can you keep it out?• What is the risk of wildlife, fomites, etc.

BVDV PI BVDV Non PI

Test + 29 60 89

Test - 1 2910 2911

30 2970 3000 cattle

BVD PCR Sensitivity ~98, Specificity ~98

Prevalence of BVD PI = 1%

Conclusion: Don’t bother testing, you’ll miss one of the PIs and the virus will persist in the herd

PPV = (29/89) 33% NPV = (2910/2911) 99%

BVD PI BVD

Non-PI

PCR Test + 5 (2 heifers, 3

newborn calves)

8 (negative on multiple

follow-up tests)

13

PCR Test - ? 3653? 3653?

? 5 ? 3661 3664

2 x 2 table of actual herd test

Follow-up testing • Precolostral serum sampling on 450 newborn

calves after the test and removal of BVDV PI cattle.• All 450 were negative by PCR• Two calves tested positive for BVDV antibody and

had less than 400 mg/dl of total serum immunoglobulin.– Prior to PI removal 12/226 (5.3%)– After PI removal 2/450 (0.4%)

PI characterization and sequence

PI Exposed pregnant

cattleDam of PI

Location during 1st trimester

Genetic sequence

7771 (16-month-old)

YesPurchased heifer #243

Unknown 1b

8527 (6-month-old)

NoPurchased

heifer #1160Unknown 1a

Bull calf No Home raisedExposed to

7771Identical to

7771

Heifer calf No Home raisedExposed to

7771Identical to

7771

Bull calf No Home raisedExposed to

7771Identical to

7771

Far-off Dry cows

Close-up dry cows

Heifers bred AI

Home of 7771

Heifers with a bull