DNA markers can speed selective dry cow therapy

Roger L. Saltman, DVM
RLS Management Solutions LLC
Selective dry cow therapy protocols can be effective at reducing the use of antibiotics without negatively impacting udder health.

For several years, the U.S. dairy industry has been endeavoring to reduce the use of antibiotics on dairy farms. It’s popular from a consumer standpoint; consumers are generally in favor of fewer antibiotics used in the production of food. It’s also popular from an animal health standpoint as there are situations where an animal can recover from a disease challenge on its own without assistance or without the need for antibiotic therapy.

A significant portion of antibiotic use on dairy farms is treating or preventing mastitis. In the past, blanket antibiotic therapy was used at dry off to cover a wide range of potential mastitis-causing pathogens. More recently, the lack of available antibiotic dry cow tubes has led many dairymen to consider a more selective approach.

Two categories of candidates

This selective dry cow therapy approach categorizes cows into two groups. Those cows with a history of clinical mastitis or subclinical infection at dry off receive an antibiotic treatment along with a teat sealant. Those cows relatively free of mastitis incidents do not receive an antibiotic therapy and just get the teat sealant.

Selective dry cow therapy protocols can be effective at reducing the use of antibiotics without negatively impacting udder health. However, it’s not for every dairy. Clinical mastitis cases need to be under control, and annual bulk tank somatic cell counts need to be under 250,000 cells/ml. There also needs to be well-trained personnel who can administer teat sealants and dry cow therapies aseptically in order to prevent new infections post-dry off. Personnel also need to be available to make decisions about which cows to treat based on screening data. Finally, someone needs to be able to monitor program effectiveness and make the necessary adjustments.

With these factors in place and mastitis cases under control, producers can decide which cows fit into the two categories (antibiotic or non-antibiotic treatment). Decisions about which dry-off approach is appropriate for each cow can be determined by the use of a somatic cell count/previous clinical mastitis algorithm or by a culture-based protocol.

Algorithm or culture

The algorithm method takes into account the degree to which cows have experienced mastitis during the lactation. Cows with a somatic cell count under 200,000, no clinical mastitis within the previous 14 days of lactation and under two clinical mastitis cases during lactation could receive just the teat sealant. All cows exceeding any of these thresholds would receive both an antibiotic and teat sealant at dry off.

The culture-based method is just as effective but requires another step to identify specific pathogens that could be causing subclinical mastitis. In this situation, samples are taken from each cow several days prior to their last milking and those samples are cultured to identify the presence of mastitis-causing pathogens. Each quarter can be sampled individually, or milk from all 4 quarters can be comingled into one sample for analysis.

The culturing process can be initiated in one of two ways. The milk sample can be packaged and sent to a lab for analysis; this usually takes about two to three days to receive results. Alternatively, a dairy can have an on-farm culturing lab that can speed the culturing process by eliminating the shipping time. These on-farm labs need to be stocked with the proper culturing equipment, and a person must be properly trained to culture the samples.

A faster way to “culture”

An alternative to culturing has emerged that speeds the process of accurately identifying mastitis pathogens without the delays associated with culturing. Milk can be taken from each quarter at the next-to-last milking and comingled into a single sample. Then, instead of culturing, the sample can be tested for the presence or absence of DNA material from either Strep or Staph bacteria by using a PCR system from Acumen Detection. This alternative significantly reduces the time it takes to make a treatment decision (<3 hours), leaving plenty of time to decide whether or not a cow needs antibiotic dry treatment at the final milking.

As with any program, monitoring is important to identify areas of success and opportunities for improvement. Producers should monitor bulk tank samples to identify mastitis-causing pathogens as well as routine culturing or PCR of cows with clinical and/or chronic mastitis. In addition, a successful dry cow program can be evaluated by monitoring the incidence of mastitis during the dry cow period and within the first four weeks after calving.

Any dry cow therapy program needs to be developed with the advice and counsel of your veterinarian. Veterinarians can also play an active role in setting up and maintaining a monitoring program to determine the need for ongoing improvements. Finally, a veterinarian should be involved in the training and evaluation of personnel assigned to administering intramammary antibiotics or teat sealants to ensure proper aseptic procedures are being followed.