title: Effect of natural infection with minor pathogens on susceptibility to natural infection with major pathogens in the bovine mammary gland.
abstract: OBJECTIVE
  To evaluate the effect of natural udder infection with minor pathogens on subsequent natural infection with major pathogens.
  
  
  METHODS
  7 dairy herds with low bulk milk somatic cell count.
  
  
  METHODS
  During a 20-month prospective study, milk samples were collected from diary cows at regular intervals and from quarters with clinical signs of mastitis. Incidence of intramammary infection was calculated in uninfected quarters and in quarters infected with minor pathogens. A within-cow, matched case-control analysis was used to evaluate the effect of minor pathogens on subsequent infection with major pathogens.
  
  
  RESULTS
  Quarters infected with minor pathogens had higher somatic cell count than did uninfected quarters. In quarters infected with Corynebacterium bovis, the rate of infection with major pathogens was lower, whereas in quarters infected with coagulase-negative Micrococcaceae, the rate of infection with major pathogens was higher than that in uninfected quarters. From the within-cow comparison, it appeared that, in quarters infected with minor pathogens, infection with major pathogens was significantly lower than that in comparable control quarters not infected with minor pathogens.
  
  
  CONCLUSIONS
  Minor pathogens have a protective effect against infection with major pathogens. The protective effect of C bovis against subsequent infection with major pathogens appears to be greater than the effect of coagulase-negative Micrococcaceae.
authors.affiliation: Department of Herd Health and Reproduction, Faculty of Veterinary Medicine, Utrecht University, The Netherlands.
authors.forename: T J
authors.initials: TJ
authors.lastname: Lam
authors.forename: Y H
authors.initials: YH
authors.lastname: Schukken
authors.forename: J H
authors.initials: JH
authors.lastname: van Vliet
authors.forename: F J
authors.initials: FJ
authors.lastname: Grommers
authors.forename: M J
authors.initials: MJ
authors.lastname: Tielen
authors.forename: A
authors.initials: A
authors.lastname: Brand
mesh_terms: D000818:Animals; D016022:Case-Control Studies; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology; D003352:Corynebacterium / Q000302:isolation & purification / Q000502:physiology; D003354:Corynebacterium Infections / Q000150:complications / Q000503:physiopathology / Q000662:veterinary*; D004198:Disease Susceptibility; D004926:Escherichia coli / Q000302:isolation & purification / Q000502:physiology; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*; D005260:Female; D015994:Incidence; D008321:Mammary Glands, Animal / Q000382:microbiology* / Q000473:pathology; D008892:Milk / Q000166:cytology; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000302:isolation & purification / Q000502:physiology; D013290:Streptococcal Infections / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*; D013291:Streptococcus / Q000302:isolation & purification / Q000502:physiology