title: Characteristics of dairy cows during episodes of bacteriologically negative clinical mastitis or mastitis caused by Corynebacterium spp.
abstract: OBJECTIVE
  To use clinical and lactational characteristics to determine whether bacteriologically negative (BN) clinical mastitis episodes are more apt to be caused by gram-negative or gram-positive bacteria, and to investigate severity of clinical mastitis caused by Corynebacterium spp (COR).
  
  
  METHODS
  Case series.
  
  
  METHODS
  300 clinical mastitis episodes affecting 123 dairy cows vaccinated against lipopolysaccharide core antigens.
  
  
  METHODS
  Cows were examined at onset of clinical mastitis, and 23 characteristics, including rectal temperature, heart rate, rumen contraction rate, degree of dehydration, udder and milk characteristics, lactation number, stage of lactation, and season of year, were recorded. Milk production and milk constituent concentrations before onset of mastitis were obtained from herd records. Values for cows with BN milk were compared with values for cows from which milk yielded gram-negative bacteria (GNB) or gram-positive cocci (GPC); logistic regression was used to predict which pathogen type was causing BN mastitis. Characteristics for cows from which milk yielded COR were compared with those of cows from which milk was BN or yielded GPC.
  
  
  RESULTS
  BN clinical mastitis episodes differed significantly from episodes caused by GPC, and were similar to, but milder than, episodes caused by GNB. COR were isolated in a substantial proportion of mastitis episodes, but clinical signs were milder than when GPC were isolated.
  
  
  CONCLUSIONS
  Most BN mastitis episodes in cows receiving lipopolysaccharide core antigen vaccines appear to be caused by low-grade infection with GNB, and treatment and management decisions should be made accordingly. The COR may be economically important clinical mastitis pathogens in some herds.
authors.affiliation: Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana 61802, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Morin
authors.forename: P D
authors.initials: PD
authors.lastname: Constable
mesh_terms: D000818:Animals; D002417:Cattle; D003354:Corynebacterium Infections / Q000382:microbiology / Q000503:physiopathology / Q000662:veterinary*; D005260:Female; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000503:physiopathology / Q000662:veterinary*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology / Q000503:physiopathology / Q000662:veterinary*; D007774:Lactation; D016015:Logistic Models; D008321:Mammary Glands, Animal / Q000473:pathology; D008414:Mastitis, Bovine / Q000382:microbiology* / Q000503:physiopathology; D008892:Milk / Q000382:microbiology; D012720:Severity of Illness Index