Precolostral screening of newborn calves for the detection of BVDV in large dairy herds Jeremy Schefers, DVM Minnesota Veterinary Diagnostic Laboratory
Jan 12, 2016
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