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

2. Herds with 500+ cows represent 50% of the total dairy cows on 4
Herds with 500+ cows represent 50% of the total dairy cows on 4.5% of all farms

3. 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”

4. Bovine gestation and fetal infection with non-cytopathic BVDV
Conception
Day 80
Day 120
Birth Day 280
EED PI
Seroconversion
Day ~120 – term:
These calves have BVDV antibodies at birth and prior to colostrum feeding. “Precolostral serum antibodies”
Conception to 80 days: fetal loss
Day Gestation:
Development of BVDV PI calf.

5. PI versus fetal seroconversion
Diagnosing 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%.
90% confidence 44 animals
95% confidence 58 animals
EED
EED PI
Seroconversion
Day 0
Day 80
Day 120
Day 280

6. Precolostral sampling - Compliance

7. Precolostral sampling
Herd
Calves sampled
No. (%) antibody +
No. (%) RT-PCR +
PI (%) CA
236
19 (8.1)
4 (1.8)
2 (0.9)
210
14 (6.7)
3 (1.4)
0 (0) MN
226
12 (5.3)
1 (0.4)
289
20 (6.9)
16 (5.5)
5 (1.7)
Total
961
65 (6.8)
25 (2.6)
8 (0.8)

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

9. 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

10. Chapter 3: Detection, characterization and control in a large dairy herd
Calves sampled
No. (%) antibody +
No. (%) RT-PCR +
PI (%) CA
236
19 (8.1)
4 (1.8)
2 (0.9)
210
14 (6.7)
3 (1.4)
0 (0) MN
226
12 (5.3)
1 (0.4)
289
20 (6.9)
16 (5.5)
5 (1.7)
Total
961
64 (6.8)
25 (2.6)
8 (0.8)

11. 480 cows 480 cows Maternity Fresh cow Parlor Heifers Close-up dry cows
Far-off dry cows

12. Direct contact with another 500+ New introductions are common
500 lactating dairy cows
Direct contact with another 500+
New introductions are common
Biosecurity protocols are uncommon

13. 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

15. 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.

16. BVD PCR Sensitivity ~98, Specificity ~98
Prevalence of BVD PI = 1%
BVDV PI
BVDV Non PI
Test + 29 60 89
Test - 1
2910
2911 30
2970
3000 cattle
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%

17. 2 x 2 table of actual herd test
BVD PI
BVD
Non-PI
PCR Test +
(2 heifers, 3 newborn calves)
(negative on multiple follow-up tests) 13
PCR Test - ?
3653?
? 5 ?
3661
3664

18. 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%)

19. PI characterization and sequence
Exposed pregnant cattle
Dam of PI
Location during 1st trimester
Genetic sequence
(16-month-old)
Yes
Purchased heifer #243
Unknown 1b
(6-month-old) No
Purchased heifer #1160 1a
Bull calf
Home raised
Exposed to 7771
Identical to 7771
Heifer calf

20. Heifers with a bull
Heifers bred AI
Home of 7771
Close-up dry cows
Far-off Dry cows