Bulk milk somatic cell counts and bovine viral diarrhoea virus (BVDV) infection in 7252 dairy herds in Brittany (western 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.
Beaudeau
F
F
Unit of Animal Health Management, Veterinary School-INRA, BP 40706, 44307 Nantes Cedex 03, France. beaudeau@vet-nantes.fr
Fourichon
C
C
Robert
A
A
Joly
A
A
Seegers
H
H
D000818:Animals; D001912:Bovine Virus Diarrhea-Mucosal Disease / Q000453:epidemiology* / Q000276:immunology / Q000821:virology; D002417:Cattle; D003612:Dairying; D005260:Female; D005602:France / Q000453:epidemiology; D008892:Milk / Q000166:cytology* / Q000276:immunology; D011159:Population Surveillance