Salmonellosis is an increasing problem on some dairies due to a variety of factors. In particular, Salmonella dublin is host-adapted for cattle and can develop readily into the carrier state in cattle. “Undoubtedly, there has been an increase in both the awareness of the disease as well as the number of cases of salmonellosis in recent years,” notes Simon Peek, BVSc, PhD, Dipl. ACVIM, University of Wisconsin-Madison. “There is little doubt from several studies that the prevalence has increased in this country over the last 10–20 years.”

Peek adds that numerous factors have been examined as potential risks for Salmonella prevalence in some large, multi-state studies, and it appears that larger herd size is one of the more repeatable factors. “Biosecurity is a bigger challenge for larger dairies when compared to smaller herds due to housing systems, the frequent need to purchase animals or at least raise heifers off site, and the inevitable exposure risks for what is a feco-orally transmitted disease.”

Peeks says there is an increased potential for exposure within housing, in the parlor, or in other areas where cattle are located. “We do know that cattle around the time of calving are more immunologically susceptible to new infections and that sick, lame and older cattle are more likely to be shedding Salmonella without necessarily showing typical signs, hence managing cattle with these facts in mind can be helpful in prevention.”

Risk factors for Salmonella

  • More frequent in dairy herds than beef herds, mixed dairy and beef herds, and calf herds.
  • Outbreaks more common in calving season, and also appear to be more common in the summer months.
  • Outbreaks more common in large herds.
  • Purchasing cattle from “dealers” rather than source herds.
  • Expansion.
  • Confinement.
  • Sick and calving cows commingled.
  • Wild birds having access to feed storage facilities.
  • Antimicrobial use prior to or at the time of exposure.
  • Use of flush-water systems.
  • Feeding brewers’ products, animal by-pass protein sources, vegetable or other fat sources to lactating cows.
  • Allowing commodity storage areas, particularly those that drain poorly or can retain moisture, to become wet.

Losses due to Salmonella

Because Salmonella can cause reproductive losses, typically abortion in late pregnancy, and/or diarrhea in cattle of any age, any sudden occurrence of either of these problems in a number of cattle over a short period of time should alert producers to the possibility of disease. Peek notes that what is more challenging diagnostically is the isolated case of diarrhea or abortion. “Increasingly, we also have concerns over the potential subclinical impact of Salmonella exposure and infection on production and general cow health. Because Salmonella is present in the environment of so many dairies, it is inevitable that cattle will be exposed, and even though they may not become clinically ill, the infection may be a sufficient drain on them to lessen production, fertility or resistance to other diseases.”

Clinical signs of Salmonella infection

  • Pyrexia
  • Lethargy, depression
  • Decreased milk production
  • Anorexia
  • Dehydration
  • Increased salivation
  • Diarrhea progressing to dysentery
  • Clinically inapparent carriers can shed for up to 18 months (non S. dublin carriers)

Shedding duration for Salmonella serotypes other than S. dublin can probably be measured in weeks to a few months, whereas S. dublin can be lifelong in a proportion of affected, recovered cattle, Peek says. “These time frames make it impractical for many farms to segregate long enough to be confident that the risk of infecting other cattle is reduced to zero,” he states.

Currently the only way to identify infected cattle is by fecal culture, serologic blood testing for S. dublin no longer being available, and fecal culture can be insensitive enough that even extensive (and expensive) testing protocols in calves and cows will miss many infected animals. For these reasons, Peek says, management changes that reduce exposure of susceptible populations at key times to feces from other cattle are relevant and important. “Not commingling cattle of different ages and arranging housing so that there is no contact between sick cows and fresh or transition cows and the absolute minimum time possible for contact between new born calves and adults are important components of this.”

Salmonellosis and calves

Salmonella infection in calves typically produces diarrhea, but in neonates less than 1 month old, it can also cause a true septicemia where the organism penetrates the bloodstream and spreads to cause multiple organ failure. This can be exacerbated by inadequate colostrum intake but does not require failure of passive transfer to occur. “Salmonella dublin infection in calves, which appears to be on the rise in many dairy areas in the United States, also has the propensity to cause pneumonia, particularly in group-housed weaned calves,” Peek explains. “Salmonella outbreaks in calves can occur at any age but undoubtedly the majority of non-dublin outbreaks that we see are in pre-weaned individuals.”

Saliva and or abomasal/rumen contents can be sources of enteric pathogens; therefore it is very important to disinfect common-use equipment such as esophageal feeders and bottles between calves and also to let them dry between uses.

Because Salmonella can survive for protracted periods, especially in warm, moist organic material, thorough cleaning and allowing ultraviolet irradiation and drying to occur between occupants of calf hutches can be very important parts of Salmonella control in calves. Avoiding nose-to-nose contact and nose-to-rear end contact is also important. “Relocating hutches to different sites or using an apron under the hutches that can be thoroughly cleaned is also relevant because the organism may persist in the soil under/around a hutch regardless of how well-cleaned the housing itself is.”

Take measures against zoonoses

“With all zoonotic diseases, it is a highly relevant part of our broader responsibility as veterinarians to educate family members, employees and those in contact with cattle about the risks of Salmonella infection,” Peek suggests. “Personal hygiene (frequent hand washing for example) and the avoidance of unpasteurized products are two simple and key areas we always focus on, but especially during outbreaks or on endemic farms an awareness of the signs of salmonellosis in people is something we should always reinforce in those who work with cattle.”

Avoiding zoonoses

  • Outer layer of protective clothing is left at farm or at the site of the contamination.
  • Use gloves and protective wear.
  • Do frequent hand washing.
  • No eating or drinking in work areas.
  • Don’t drink raw milk. 

Salmonella control strategies

The strategies implemented to control Salmonella infections should be prioritized and focused on minimizing the source of infection and maximizing host immunity. They can include:

  • Adopt an all-in/all-out system in calf and heifer raising facilities.
  • Maintain a closed herd or make purchases from low-risk herds.
  • Manage new additions to minimize stress and infection of residents.
  • Minimize stress by feeding good rations, providing adequate time and space for transitions and maintain clean, uncrowded maternity pens.
  • Use different facilities for calving cows and sick cows.
  • Avoid adult to calf contact. Isolate heifers from the lactating herd.
  • Disinfect waters in high risk areas (dilute bleach twice daily).                      
  • Scrape manure, remove organic debris, disinfect clean, non-porous surfaces and expose to sun or UV light.
  • Minimize fecal contamination of feedstuffs, feeding surfaces, water troughs and equipment.
  • Drain and level areas that collect water.
  • Allow no access to pond water or feeding areas cohabited by birds and waterfowl.
  • Isolate the entire group in which affected cows commingle.
  • There should be no shared bunk spaces, water source, feeding or manure handling equipment. Left over TMR from the cows should be not be fed to the heifers.
  • Segregate Salmonella test-positive cows at calving.
  • Do not use colostrum or milk from test-positive cattle.
  • Manure-handling equipment is not used to handle feed and it is kept out of feed lanes or food storage areas.
  • Make certain that feed delivery vehicles do not travel through manure or across manure scraping lanes.
  • Control rodents and birds.
  • You must be vigilant about waste management, control of effluent, and the distribution of recycled flush water.
  • Vaccination will not stop infection but selected vaccines may reduce the severity of infection and curtail the mortality rate. Vaccines are no substitute for management to reduce contamination and decrease stress.
  • Pasteurization of waste milk and colostrum; even refrigeration will contain growth of salmonellae in contaminated colostrums and waste milk.

Source: Simon Peek BVSC, PhD, Dipl. ACVIM

11 action steps against Salmonella

From the 1999 American Association of Bovine Practitioners Food and Water Symposium, 11 action steps were suggested to tackle herd salmonellosis:

  1. Break the fecal–oral transmission link by minimizing fecal contamination of feedstuffs, feeding surfaces, water troughs and equipment.
  2. Maximize host resistance of susceptible animals (transition animals and newborns) and minimize exposure dose.
  3. Control anything in the livestock environment that can perpetuate the organism  —  rodents, flies, nuisance birds and dogs.
  4. Because many of the infected animals are subclinical, in an outbreak, handle all animals as if they were shedding.
  5. Implement a sound sanitation program based on cleaning all organic matter  —  feces, saliva, milk and blood  —  prior to use of disinfectants (orthophenylphenol on surfaces and boots and chlorhexidine for equipment).
  6. Look for development of newer vaccines that target signaling pathways and other unique strategies rather than relying on conventional bacterins for prevention and control.
  7. A healthy intestinal environment gives cattle a competitive resistance. Survival of competitive lactobacilli offer resistance to calves. Maintain the normal gram negative flora (< 1% of the GI mass of bacteria and these are primarily anaerobes) by minimizing oral antibiotic therapy.
  8. Maximize rumen function by consistent DMI in transition and parturient cows. VFA’s are toxic to Salmonella.
  9. Recognize extended survival time of salmonellae in the environment and deal with potential for spread 4 to 5 years after outbreak.
  10. Minimize the chance for salmonellae to replicate by minimizing time in moist, warm environmental conditions. Mix feeds in smaller batches and feed soon after mixing. Don’t feed the waste TMR to young stock.
  11. Warn farm families about zoonotic potential and assist them in implementing steps to minimize the risk.