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13. Contagious Mastitis

Possible antibiotic treatments for Streptococcus agalactiae

  • Intramammary penicillin
  • Intramammary amoxicillin
  • Intramammary cephapirin
  • Intramammary pirlimycin
  • Intramammary ceftiofur

 

Poor antibiotic choices for Streptococcus agalactiae

  • Intravenous oxytetracycline
  • Intramuscular oxytetracycline
  • Intramammary gentamicin
  • Subcutaneous florfenicol
  • Intramuscular ceftiofur   

 

Dr. Keller:  “Now we need to decide which cows should receive our intramammary treatment.  In order to avoid antibiotic residues, we do not want to treat cows that are about to be culled due to low production, old age or other problems.  Chronically infected cows are much less likely to respond to treatment and are more likely to become re-infected, so these cows should probably be culled instead of treated.  Cows that are late in lactation should be dried off a few weeks earlier than originally planned, and given an antibiotic dry treatment instead of an antibiotic licensed for lactating cows.

sagattil_section.jpgA picture of a sagittal section of a cow’s udder to demonstrate distribution of a dye administered by intramammary infusion, in the front quarter(non-mastiticleft of red line) or the rear quarter (mastitic, right of red line).  The front resulted in widespread diffusion of the dye, while the dye poorly diffused in the rear quarter.  The limited diffusion of the dye in the mastitic quarter is due to fibrotic change and abscess formation.  This demonstrates why some forms of mastitis are not easily treated with antibiotic intramammary infusions. 

The more difficult problem is Staphylococcus aureus.  To control Staphylococcus aureus, we need to identify the cows that have only recently been infected because these are the best therapeutic candidates.  Chronic infections – which we identified earlier based on SCC linear scores - have a much lower likelihood of responding to treatment.  Cows that are chronically infected with Staphylococcus aureus are very difficult to cure by antibiotic treatment because of the micro-abscesses and scar tissue that this particular organism causes in the mammary tissue.  We only want to use antibiotics for those animals that are most likely to respond.  Most cows that are chronically infected should be culled.  If we do not identify the chronically infected cows and just treat all the cows with antibiotics, the chronically infected cows will not be cured and will remain a source of the Staphylococcus aureus for other cows in the herd.  Finally, the infected cows that are not culled should be segregated from the rest of the herd and milked last, or with separate equipment, to prevent spread to the rest of the herd.

 

 

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