Subclinical mastitis is a stealthy thief, showing no visible signs of entry. Yet, there are indirect clues — in the form of elevated somatic cell counts — that show a burglar has broken in.     

When a high percentage of cows freshen with subclinical mastitis, you know there’s been a security breach during the dry period. So, focus much of your effort on the dry cows. Find ways to reduce pathogen exposure, as well as make cows more resistant to these invaders.   

Here are some suggestions: 

Reduce exposure

“Research has taught us that the mammary gland is particularly susceptible to new intramammary infections during the first two to three weeks after dry-off and during the last two weeks prior to calving,” explains Sandra Godden, veterinarian at the University of Minnesota.

To lower subclinical cases, expose the teat to the least amount of germs possible during these critical phases. Sounds simple, but it’s not always done well, says Leo Timms, extension dairy specialist at IowaStateUniversity.

Remember, bacteria need access to warm, moist conditions and organic matter. You can knock down its support system by keeping the cow’s environment clean and dry. Assess where you can make improvements in these key areas:

  • Bedding choice, cleanliness and maintenance.
  • Free-stall hygiene and maintenance.
  • Stall dimensions and usage.
  • Ventilation. Ventilation not only reduces moisture, thereby reducing bacterial growth, but it also facilitates cow cooling. This reduces heat stress that can weaken the cow’s immune system and make her more susceptible to mastitis, Godden says.

Increase resistance

Research shows that the dry cow may need extra help to keep bacteria from invading her udder. In one multi-university study presented at the 2003 NMC annual meeting, 50 percent of teat ends were still open one week after dry-off. This delay in keratin-plug formation gives bacteria easy access to the teat canal. Remember, it only takes one single germ acting in “secret-agent” style to infiltrate the teat, Timms says.

Resistance is the key. Several tools can help you lower the incidence of subclinical mastitis in your herd. Work with your veterinarian to decide which tools you should use to bolster your dry cows’ resistance to invaders.

  • Dry-cow therapy. Use the dry period to cure existing subclinical infections with a dry-cow antibiotic therapy. This helps build resistance by preventing new infections, too.
  • Internal and external blocks. Set up a firewall that keeps germs out of the teat. Consider how best to incorporate physical barriers like an external barrier dip and internal teat sealant into your subclinical-prevention arsenal.
  • Vaccines. Vaccines bolster a cow’s immune response to challenges in her environment. Determine if a gram-negative or core-antigen vaccine is the right fit for your operation.
  • Early dry off. This gives the mammary gland longer access to the benefits of dry-cow antibiotic therapy. If the cell count for an individual cow is high, talk to your veterinarian about other options you might consider at dry off.

Remember, to get good results from these tools, your management program must also include proper nutrition, a comfortable environment, good ventilation and appropriate temperature control, Timms adds. It takes all of these tools working in tangent to provide an effective defense against subclinical mastitis.