Disease outbreaks caused by salmonella spp. now occur in dairy herds across the country. Salmonellosis is a major concern for the dairy industry because the bacteria can invade almost any species — including humans — and the infections produced can be very severe. Therefore, minimizing its occurrence within in the food chain is very important. 

In recent years, salmonella strains that are resistant to most of the available antibiotics have emerged, making treatment of veterinary or human cases very difficult.  Called multiple drug resistant, or MDR, these strains are one of the main reasons our industry has faced increasing pressure to limit antibiotic use in feed.

However, several new tools combined with improved knowledge have enhanced our ability to help control the spread of this disease in dairies. Here’s what you need to know. 

What it is

Salmonellosis is a disease caused by one of multiple strains of Salmonella enterica. The bacteria invade the lining of the intestine and produce severe diarrhea, often leading to death, particularly in neonatal calves and transition cows. The bacteria also can cross the lining of the intestine, enter the bloodstream and attack other organs.  In young calves, this often leads to septicemia or pneumonia.

The primary mode of transmission is fecal-to-oral. Cows with diarrhea are obvious sources of the bacteria, and a hospital pen used for both sick and fresh cows is one of the greatest risk factors for a salmonella outbreak. Newborn calves and fresh cows have a lowered immune system that makes them more susceptible. 

The bacteria can survive in the environment for a very long period of time — in some cases, at least five years. Most manure-storage systems permit survival and even multiplication of the bacteria, and liquid-flush systems are particularly risky.

Control measures

To control the spread of salmonella infections, you must maximize the resistance of susceptible animals and minimize the number of bacteria to which an animal is exposed. Use these steps:

  • Vaccines.  With several strains of virulent salmonella, protective immunity from a vaccine has been difficult to achieve.  Recent technology appears to be much more effective. Salmonella need iron to survive and multiply. The bacteria have a receptor site for iron uptake that animal cells lack. A vaccine that blocks this receptor site (siderophore receptor and porin proteins, or SRP proteins) essentially starves the bacteria of iron, and effectively controls the clinical disease caused by all strains of salmonella. 
  • Feed additives. Some feed additives are clinically useful to help control outbreaks of salmonella in herds. One is mannan oligosaccharides (MOS), a yeast-cell-derived carbohydrate that may both bind salmonella bacteria and stimulate immunity at the intestine. And some species of Lactobacillus spp. will stimulate local immunity and may function as a competitive inhibitor to salmonella bacteria in the intestine.
  • Dry matter intake. When dry matter intake is depressed, salmonella bacteria survive and multiply in the rumen. Therefore, strategies that improve transition-cow dry matter intake and maintain effective fiber concentrations, both pre- and postpartum, are valuable in limiting clinical outbreaks.
  • Clean environment. Disinfecting contaminated areas, maintaining a clean calving environment, and not using feedstuffs that are contaminated with salmonella may seem like obvious steps, but they must be done diligently every day.
  • •Manage shedders. In a salmonella outbreak, clinical cows are the “tip of the iceberg.” Subclinically infected cows and heifers also shed the organism and can be a significant source of infection.  Assume that all animals in the herd are possible shedders and manage them accordingly. The SRP vaccine has been reported to decrease fecal shedding, so its ongoing use in a herd that has experienced an outbreak is indicated. In addition, remember that oral and nasal secretions also can be a source of salmonella organisms. This is particularly true in calves, so cross-contamination of buckets and feeding utensils can be a problem.
  • Separate fresh and sick cows. While I listed this earlier as the biggest area of risk on farms, too many fresh cows are still intermingled with sick cows.

Salmonellosis is a devastating disease that can establish itself within a dairy herd from multiple possible directions. If it occurs in your herd, use good management and hygiene, as well as the new tools to enhance immunity and stop the spread of disease.

Brian J. Gerloff is a veterinarian and operates Seneca Bovine Services in Marengo, Ill.