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3. Contagious Mastitis

 As another way to look for evidence of subclinical mastitis in the herd, Dr. Keller checks the bulk milk tank SCC report.  A reasonable goal for bulk milk tank SCC is < 200,000 cells per ml.  Federal and state regulations require that consumers not purchase Grade A milk from dairies that have a bulk milk SCC > 750,000 cells per ml.  Dr. Keller confirms that the bulk milk tank SCC has been slowly increasing and is now > 300,000 cells / ml.  

Common mastitis pathogens (2):
  • Staphylococcus aureus
  • Streptococcus agalactiae
  • Streptococcus uberis
  • Streptococcus dysgalactiae
  • Escherichia coli
  • Klebsiella sp.
  • Coagulase negative staphylococci

Less common  mastitis pathogens:
  •     Corynebacterium bovis
  •     Mycoplasma spp.
  •     Pseudomonas aeruginosa
  •     Pasteurella multocida
  •     Serratia marcescens
  •     Bacillus sp.
  •     Nocardia



Contagious Udder Pathogens (2):


  1. Streptococcus agalactiae
  2. Staphylococcus aureus
  3. Mycoplasma spp.
  4. Corynebacterium bovis
  5. Common characteristics of the contagious udder pathogens:
  • Infection with these pathogens primarily result in subclinical udder infection (except Mycoplasma bovis which may also cause outbreaks of clinical mastitis)
  • Primarily infect the gland after colonization of the skin (or from bacteremia in the case of Mycoplasma bovis).
  • These pathogens commonly infect the gland via teat impact (moving up the teat canal) if the milking equipment is not functioning properly.
  • Treatment of cows infected with these contagious udder pathogens is often thwarted because cured cows will likely get re-infected quickly unless management changes are adopted to prevent cow-to-cow transmission.



Environmental Udder Pathogens (3):

1.    Coliforms : Escherichia coli, Klebsiella, Enterobacter

2.    Streptococcus spp. (other than S. agalactiae)

3.    Coagulase negative Staphylococcus spp. (other than S. aureus)

a.    These are more likely to be resident skin flora.

4.    Other Gram-negative rods (Pseudomonas, Proteus)


Environmental Udder Pathogens are:

a.    The primary cause of clinical mastitis

b.    May also cause subclinical mastitis

c.    Also transiently colonize the skin on the teats and udders


5.    Examples of mastitis pathogens with identified environmental risk factors (3)

a.    Pseudomonas:  Are associated with contaminated water from wash hoses or hot water heaters.

b.    Klebsiella:  Are associated with sawdust or shavings used as bedding.

c.    Streptococcus uberis:  Are associated with straw bedding.




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