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Should I be considering selective dry cow therapy on my farm?

Jackie Boerman – Purdue University

Antibiotic therapy at dry off has been widely adopted by the dairy industry to reduce the number of new mastitis infections during the dry period. The practice of intramammary antibiotic infusions was introduced over four decades ago and currently accounts for approximately one-third of the antibiotics used on dairy farms. Dry cow therapy has been shown to cure existing infections and reduce the risk of clinical mastitis and high somatic cell counts in early lactation. Many farms opt to utilize intramammary antibiotics on every cow at dry off, referred to as blanket dry cow therapy, to act as insurance against potential mastitis risks. Recent approaches, being tested on-farm and in research settings, have considered including information about the individual cow in the decision of whether or not to administer dry cow therapy. 

Differentiating between which cows may benefit from antibiotics at dry off and which cows may not need antibiotics is referred to as selective dry cow therapy.  Ideally, selective dry cow therapy would reduce the amount of antibiotics used on farm without compromising future cow health and production.  Farms that may want to consider if selective dry cow therapy would work for them include:

  1. Consistent bulk tank somatic cell counts below 250,000 cells/mL

  2. Low incidences of Staph. aureus and Strep. agalactiae, of which antibiotics would be effective

  3. Utilize teat sealants at dry off

  4. Can utilize records to determine if the program is working

If farms meet these criteria and are considering selective dry cow therapy, there are 2 different approaches to determining to which individual cows to administer antibiotics, historical data driven or milk culture driven decisions. Utilizing a historical data approach, individual cows that have somatic cell counts < 200,000 cells/mL for all tests during their current lactation, have not had clinical mastitis cases within the last month, and have had less than 2 clinical mastitis cases during the last lactation, the farm would not administer antibiotics and just administer teat sealant. Whereas, individual cows with somatic cell counts >200,000 cells/mL for any test during their lactation, have had a clinical mastitis case within the last month of lactation, or have had 2 or more cases of clinical mastitis cases during their last lactation may be good candidates for receiving antibiotic therapy.  The second approach is to perform a milk culture prior to dry off and read and interpret the culture plates to determine if antibiotic susceptible bacteria are present. This method requires milk sampling, trained personnel and has additional costs associated with milk cultures, it will also identify animals that have no growth that will likely not benefit from antibiotic therapy.

Implementation of selective dry cow therapy requires increased emphasis on record evaluation, communication about which animals to treat, and documentation of which animals are treated in order to determine if this program is effective on farm. While antibiotics are effective for treating certain cases of mastitis, there are likely cows that do not require antibiotics at dry off because of their current and historical udder health. Please consult with your veterinarian about how to best implement a selective dry cow therapy on your farm if this is of interest. 

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