title: Bovine respiratory syncytial virus and bovine coronavirus in Swedish organic and conventional dairy herds.
abstract: BACKGROUND
  Infections with bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BoCV) are endemic to the cattle populations in most countries, causing respiratory and/or enteric disease. It has been demonstrated that herds can remain free from these infections for several years also in high prevalence areas. Organically managed (OM) dairy herds have been shown to have lower seroprevalence of both viruses compared to conventionally managed (CM) herds. The objective of this study was to challenge the hypothesis of a lower occurrence of BRSV and BoCV in OM compared to CM dairy herds. In November 2011, May 2012 and May 2013 milk samples from four homebred primiparous cows were collected in 75 to 65 OM and 69 to 62 CM herds. The antibody status regarding BRSV and BoCV was analysed with commercial indirect ELISAs. Herds were classified as positive if at least one individual sample was positive.
  
  
  RESULTS
  The prevalence of positive herds ranged from 73.4% to 82.3% for BRSV and from 76.8% to 85.3% for BoCV among OM and CM herds, over the three sampling occasions. There was no statistically significant difference between OM and CM herds at any sampling occasion. The incidence risk of newly infected herds did not differ statistically between OM and CM herds at any sampling occasion, neither for BRSV nor for BoCV. The incidence of herds turning sero-negative between samplings corresponded to the incidence of newly infected. Bulk tank milk (BTM) samples were also sampled in the herds and analysed. Several herds were negative on individual samples but positive in BTM. Herd-level data on production, health and reproduction were retrieved from VÄXA Sweden and the study herds were representative of the source population.
  
  
  CONCLUSIONS
  There was no difference in prevalence of or incidence risk for BRSV or BoCV between Swedish OM and CM herds. Because the incidence of herds becoming seropositive was balanced by herds becoming seronegative it should be possible to lower the prevalence of these two infections among Swedish dairy cattle herds if biosecurity is improved.
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-75007, Uppsala, Sweden. cecilia.wolff@slu.se.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Wolff
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-75007, Uppsala, Sweden. ulf.emanuelson@slu.se.
authors.forename: Ulf
authors.initials: U
authors.lastname: Emanuelson
authors.affiliation: Växa Sverige, PO Box 210, SE-101 24, Stockholm, Sweden. anna.ohlson@vxa.se.
authors.forename: Anna
authors.initials: A
authors.lastname: Ohlson
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-75007, Uppsala, Sweden. stefan.alenius@slu.se.
authors.forename: Stefan
authors.initials: S
authors.lastname: Alenius
authors.affiliation: Department of Clinical Sciences, Swedish University of Agricultural Sciences, PO Box 7054, SE-75007, Uppsala, Sweden. nils.fall@slu.se.
authors.forename: Nils
authors.initials: N
authors.lastname: Fall
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000821:virology; D018352:Coronavirus Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D017938:Coronavirus, Bovine / Q000302:isolation & purification; D003612:Dairying / Q000379:methods*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005260:Female; D015994:Incidence; D008137:Longitudinal Studies; D058871:Organic Agriculture; D015995:Prevalence; D011446:Prospective Studies; D018357:Respiratory Syncytial Virus Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D018112:Respiratory Syncytial Virus, Bovine / Q000302:isolation & purification; D016036:Seroepidemiologic Studies; D013548:Sweden / Q000453:epidemiology
chemical_list: D000914:Antibodies, Viral