Selective dry cow therapy revisited
Author: Roger L. Saltman, DVM, MBA
In recent weeks, several dry-off antibiotic treatments have gone on back order and the brands that are still available are often available only in allocated amounts. Many dairy managers are now considering Selective Dry Cow Therapy (SDCT) as a method for saving the antibiotic treatments for the cows who most need the therapy to treat udder infections at dry-off.
However, the decision to treat a cow at dry-off with an antibiotic involves careful selection; otherwise, the cow may freshen several weeks later with mastitis due to the bacteria she harbored in her udder at dry-off or one that she became infected with in the days just after she stopped being milked.
Several decision “algorithms” have been proposed to determine which cows to treat only with internal teat sealants, e.g., Orbeseal®, Lockout®, etc., and which cows should receive an antibiotic with the internal teat sealant. The University of Minnesota Extension website states that there are really two main methods for determining which cows should get both an antibiotic treatment and an internal teat sealant at dry-off: an algorithm-based SDCT Method and a culture-based SDCT Method.
The algorithm-based SDCT Method calls for using both an antibiotic and an internal teat sealant for the cows that have the following characteristics:
• Somatic cell count (SCC) greater than 200,000 at any test during the current lactation
• Any clinical mastitis cases in the last 14 days of lactation
• Two or more clinical mastitis cases during the current lactation
The culture-based SDCT Method calls for using both an antibiotic and an internal teat sealant for the cows that culture positive two days before dry-off. The problem with this approach is the need to take the samples with sufficient lead time, especially with larger herds that only dry off cows weekly. Identification, collection, shipment and lab processing time all delay action when it is top of mind.
An alternative to the second SDCT Method is to use the Acu-Polaris® PCR on a composite milk sample taken from the cow during the next-to-last milking before dry-off. The milk sample can be tested for the presence or absence of oligonucleotides (DNA material) from Staph spp. and Strep spp. by using two reagents: the Staph Reagent and the Strep Reagent. The testing only takes three hours and the results can be used with health records to support decisions about this cow.
Talk to your veterinarian about the best SDCT approach and develop a process for selection that makes the most sense on your dairy. It is critical that all teat-end infusions are done using the proper technique (sterile preparation of teat ends) and be sure to carefully monitor for
success after you start an SDCT program.
Dr. Saltman is the former chief medical officer in the cattle and equine business at Zoetis, as well as a past president of the American Association of Bovine Practitioners. He resides in Cazenovia, N.Y., where he practices veterinary medicine, as well as provides consultation services.