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

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

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 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 80-120 Gestation: Development of BVDV PI calf.

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

Precolostral sampling - Compliance

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)

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 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)

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

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

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

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.

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%

2 x 2 table of actual herd test BVD PI BVD Non-PI PCR Test + 5 (2 heifers, 3 newborn calves) 8 (negative on multiple follow-up tests) 13 PCR Test - ? 3653? ? 5 ? 3661 3664

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 Exposed pregnant cattle Dam of PI Location during 1st trimester Genetic sequence 7771 (16-month-old) Yes Purchased heifer #243 Unknown 1b 8527 (6-month-old) No Purchased heifer #1160 1a Bull calf Home raised Exposed to 7771 Identical to 7771 Heifer calf

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