Fact Sheet: Streptococcus agalactia

The Disease

Strep agalactia is a very common mastitis agent in New York. Most infected cows show no overt signs of disease, such as abnormal milk but have high somatic cell counts and decreased production. Strep ag infection can produce enough bacteria to raise the bulk tank count. Strep ag can only grow and multiply in the udder but can survive for short periods on hands, milking machine parts, and teat skin. The source of new infections is always an infected cow and the means of transmission is usually the mechanical transfer of bacteria from contaminated items such as the ones mentioned above or the mouths of suckling calves. Strep ag can be introduced into a clean herd with the purchase of an infected cow or the use of contaminated milking equipment at a fair, auction etc. To find Strep ag the milk of the cow or the bulk tank is cultured and the agent identified.

The Consequences

The impact of Strep ag is primarily in lost milk production. It does not usually cause life threatening illness, and often shows few or no obvious clinical signs of mastitis. The losses are from decreased milk, increased bacteria and somatic cell counts causing a loss of quality bonus and decline of milk quality in general. The insidious nature of the disease allows it to spread in a dairy with little or no notice until a significant problem arises such as a high bacteria or somatic cell count. Checking for new inflations, proper function and cleaning of milker parts, good sanitation with adequate hot water and proper cooling of the milk does not lead to significant improvement. If a problem of this nature is suspected bulk tank cultures can demonstrate the presence of Strep Ag in the herd. A single bulk tank culture may not reveal the infection in herds with few infected cows hence repeated culturing is indicated.

Control or Elimination

  • Bulk tank culture to identify the herd as infected
  • Sample and culture milk from all cows in the herd. This service available through QMPS
  • Infuse all infected quarters with an effective intramammary treatment
  • Follow-up with cultures to evaluate treatment
  • Cull the rare cows that do not respond to aggressive treatment.

Following the elimination of this pathogen, a practical and cost effective procedure, move to control:

  • Good milking technique
  • Pre milking udder and teat sanitation.
  • Post milking teat dipping.
  • Treatment of all clinical cases with an appropriate antibiotic.
  • Dry treating all quarters of all cows with an effective antibiotic.
  • Proper maintenance of milking equipment.
  • Sample and culture milk from all new or returning cows.