Effects of bovine coronavirus and bovine respiratory syncytial virus outbreaks on milk yield and somatic cell count

• The purpose of this study was to investigate if outbreaks of bovine corona virus (BCV) or bovine respiratory syncytial virus (BRSV) affects milk yield and somatic cell count on herd level. Seventy herds were included in the study. The herds were followed during two winter seasons, 1st of September to 30th April 2006/2007 and 2007/2008. A pooled milk sample of five primiparous cows was collected from each herd before and after each season. The milk samples were analysed for antibodies to BCV and BRSV with indirect ELISA. In the end of each season the farmers filled in a questionnaire where eventual outbreaks were described. An outbreak was defined as diarrea or respiratory symptoms affecting at least 25 per cent of the cows. Daily milk delivery reports were accessed from the dairy company and monthly bulk tank milk somatic cell counts (BTMSCC) from the Swedish official milk recording scheme. Associations between daily milk delivery and BTMSCC and outbreak status was analysed by a repeated measures mixed model. The models included an index that distinguished between herds with and without an outbreak and between weeks in relation to the day of the outbreak. The models also included the season of the year and the repeated measures within herds were accounted for by including a random effect of the herd. The first year 55 herds completed the study of which 20 experienced an outbreak of BCV and 4 of BRSV. The second year 54 herds remained in the study and the number of outbreaks was 19 for BCV and 7 for BRSV. In the questionnaire 36 of the farmers with outbreak of BCV stated that they had experienced a 5 to 50 percent (median 15) drop in milk yield in the affected cows and three could not recall. For BRSV six farmers claimed a drop of 10 to 30 percent (median 15) in milk yield, five farmers did not remember and one did not notice any difference. There where no significant differences in milk delivery or BTMSCC associated with the outbreaks, regarding both BCV and BRSV, when using the outbreak date stated by the farmer in the statistical model. The result remained non significant even when only including herds that seroconverted. It is likely that the lack of effect was due to problems in recollecting dates of outbreaks, because obvious drops in milk deliveries were observed in many herds within some weeks before or after the stated date

Ämnesord

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience (hsv//eng)

LANTBRUKSVETENSKAPER  -- Veterinärmedicin (hsv//swe)

AGRICULTURAL SCIENCES  -- Veterinary Science (hsv//eng)

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