aUnit of Animal Health Management, Veterinary School-INRA, BP 40706, 44307 Nantes Cedex 03, France bUBGDS, BP110, 56000 Vannes, France
Variations in test-day bulk milk somatic cell count (BMSCC) according to bovine viral diarrhoea virus (BVDV) infection status of the herd were quantified. Infection statuses were defined, based on bulk-milk antibodies measured twice 4 months apart. On each test-day, BMSCC was calculated as the weighted mean of the individual cow-level somatic cell counts. A total of 97,985 test-days in 7252 herds were considered. The effect of the BVDV-infection on BMSCC was assessed using mixed linear models, controlling for herd (random), proportion of primiparous cows and average days in milk on test-day. Considering test-days contemporary to the BVDV-status definition-period, the increase in BMSCC was 12,000 (P < 0.001), 27,000 (P < 0.001) and 6000 (P = 0.97) cells/ml in past-infected recently recovered, past-but-still-infected and recently infected herds respectively, compared with not recently infected herds. A carry-over effect (at least 1 year) of BVDV-infection on BMSCC was also evidenced in past-infected recently recovered, past-but-still-infected and recently infected herds.
This article was published in Preventive Veterinary Medicine, 72, F. Beaudeaua, C. Fourichona, A. Roberta, A. Jolyb and H. Seegersa, Bulk milk somatic cell counts and bovine viral diarrhoea virus (BVDV) infection in 7252 dairy herds in Brittany (western France), 163-167, Copyright Elsevier 2005.