title: Impact of bovine leukemia virus infection on neutrophil and lymphocyte concentrations in dairy cattle.
abstract: OBJECTIVE
  To determine the effect of bovine leukemia virus (BLV) infection on absolute neutrophil and lymphocyte concentrations in healthy lactating Holstein dairy cattle.
  
  
  METHODS
  Observational cross-sectional survey.
  
  
  METHODS
  311 healthy lactating Holstein dairy cattle from herds in Michigan (n = 2), Wisconsin (1), Iowa (1), and Pennsylvania (1).
  
  
  METHODS
  Whole and anticoagulated (EDTA) blood samples were collected. Serum samples were tested for antibody against BLV by use of an ELISA. Absolute neutrophil and lymphocyte concentrations were measured in EDTA blood samples with an automated hematology analyzer and manual differential cell counts.
  
  
  RESULTS
  208 cows tested positive and 103 cows tested negative for anti-BLV antibodies. Neutrophil concentration was not significantly different between BLV-positive versus BLV-negative cattle. The distribution of lymphocyte concentration was positively skewed for the entire cow population (n = 311) and the BLV-positive subset (208). In contrast, lymphocyte concentration distribution was approximately normal for BLV-negative cows (n = 103). Consequently, the presence or absence of BLV infection strongly influenced the calculated neutrophil-to-lymphocyte concentration ratio.
  
  
  CONCLUSIONS
  Results indicated that absolute lymphocyte concentration is significantly affected by BLV infection in dairy cattle. Accordingly, hematologic reference intervals should be derived from healthy animals that are not infected with BLV and patient BLV status must be considered for meaningful interpretation of lymphocyte concentration. We recommend that the calculated neutrophil-to-lymphocyte ratio be abandoned because it does not provide more information than direct comparison of patient absolute leukocyte concentration with updated reference intervals from healthy BLV-negative cattle.
authors.affiliation: Department of Pathobiology and Diagnostic Investigation and Diagnostic Center for Population and Animal Health, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA. swenson@cvm.msu.edu
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Swenson
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Erskine
authors.forename: Paul C
authors.initials: PC
authors.lastname: Bartlett
mesh_terms: D000818:Animals; D002417:Cattle; D003430:Cross-Sectional Studies; D003612:Dairying; D016583:Enzootic Bovine Leukosis / Q000097:blood* / Q000453:epidemiology / Q000473:pathology; D001909:Leukemia Virus, Bovine; D008214:Lymphocytes / Q000502:physiology*; D009504:Neutrophils / Q000502:physiology*; D014481:United States / Q000453:epidemiology