Managing what you can’t see
Controlling Salmonella Dublin remains one of the more frustrating challenges in dairy herd health. Unlike many pathogens, this host-adapted bacteria can persist quietly within a herd. As a result, detection and control become far more difficult than treating visible disease.
Recent work from Michigan State University Extension and collaborators points to a key factor producers should consider more closely: latent carrier cows and their role in transmitting infection to calves before birth.
Why Salmonella Dublin continues to matter
Over the past decade, Salmonella Dublin has become more prevalent in North American dairy systems. At the same time, concern has grown around its multidrug resistance (MDR) profile. Consequently, treatment options remain limited, while both animal health and public health risks increase.
Key challenges include:
- Limited effective antimicrobial treatment options
- Increased severity and mortality compared to other Salmonella types
- Zoonotic risk to farm workers and food systems
Because treatment options remain restricted, prevention and transmission control are essential.
The hidden problem: latent carriers
One of the most difficult aspects of Salmonella Dublin control is the presence of asymptomatic carrier animals.
These cows:
- Appear healthy
- Can shed low levels of bacteria over time
- May transmit infection directly to calves in utero
In this study, approximately 14.6% of cows screened were identified as latent carriers, although results varied widely between farms.
Therefore, some herds may face much higher hidden disease pressure than they realize.
Vertical transmission: an underappreciated risk
While producers widely recognize fecal-oral transmission, this research highlights the importance of vertical (in utero) transmission.
For example:
- 17.2% of calves from untreated carrier cows were already infected at birth
- Previous work suggests rates can be even higher under certain conditions
As a result, even strong maternity pen hygiene cannot fully prevent early infection.
Can vaccination help reduce risk?
Researchers evaluated vaccination of latent carrier cows at dry-off using a commercially available product.
The results were notable:
- Vaccinated carrier cows were five times less likely to produce infected calves
- Overall, vaccination reduced in utero transmission by 81%
- In addition, calves born to vaccinated cows showed lower antibody levels, indicating reduced exposure
However, researchers did not consistently detect bacteria in feces or colostrum at calving. This finding raises important questions about:
- Detection sensitivity
- Timing of bacterial shedding
- The relative importance of different transmission routes
What this means on farm
This research does not position vaccination as a standalone solution. Instead, it reinforces the need for a more targeted, system-based approach.
1. Start control before birth
If calves become infected in utero, post-calving strategies alone will fall short.
2. Identify higher-risk animals
Repeated testing, such as milk antibody monitoring, can help flag potential carrier cows.
3. Use vaccination strategically
Rather than applying it broadly, producers should consider vaccination:
- For known or suspected carriers
- As part of a structured dry-off protocol
4. Maintain strong biosecurity
At the same time, core practices still matter. Focus on:
- Calving pen hygiene
- Colostrum management
- Early calf separation
Together, these steps help reduce overall disease pressure.
Work with your herd team
As always, producers should work closely with their advisors when evaluating herd health strategies.
For example:
- Consult your herd veterinarian to assess Salmonella Dublin risk
- Review diagnostic tools and herd history
- Work with a nutritionist to support transition cow immunity
- Evaluate whether targeted vaccination fits your operation
The bottom line
Salmonella Dublin control continues to shift toward a preventative, system-based approach.
Ultimately, this research reinforces a key takeaway:
Managing latent carriers—especially during the dry period—can significantly reduce disease pressure in the next generation of calves.
As more becomes known about transmission dynamics, producers who focus on early intervention and targeted strategies will be better positioned to protect herd health and long-term productivity.
For more details on the study and methodology, read the full research from Michigan State University Extension.
