When your cows have issues with salmonella or E. coli, they become much less efficient.

Considering the costs that go into the precision feeding you supply your cow, when she is faced with a bacterial challenge, that’s money on the floor. Pathogenic bacteria terrorizes the gut, leaving behind a mucus layer that “nets” nutrients, preventing them from being absorbed efficiently.

Cows can have a subclinical infection of salmonella with no signs at all, or the disease can range to endotoxemia, resulting in diarrhea, pneumonia, arthritis and death. Seemingly healthy cows may also carry the organism but only shed salmonella in their manure when they are stressed, perhaps by transportation, calving or the onset of milk production. Hot weather and nutritional issues such as acidosis can also make cows more susceptible to salmonella infections. Consequently, less healthy animals that are exposed pick up on the shedding and are more susceptible to the complications of the pathogens, such as older cows, very young calves and cows with other infections. In some herds, symptoms of salmonellosis are seen in just the fresh cows while no problems are seen in other animals. In other situations, an outbreak will be seen in the whole herd due to a stress, such as hot weather or feed contamination.

Although salmonella bacteria exist to some degree on most farms, disease problems typically occur only when environmental levels of the bacteria get high enough, animal immunity is compromised, and the serotype is potent. It has been estimated that 109 to 1,010 salmonella are needed to cause infection. Good cow comfort, management and nutrition increase both milk production and resistance to salmonella and other organisms.

Multiple risk factors play precedence on the farm, and it’s a good idea to look out for these types of issues. A commonly overlooked factor in the environment of modern freestall dairies is using recycled water in manure flush systems. Feeding animal fat or brewers products also have been found to be a source of risk.


In a study by Warnick et al., significant salmonella risk factors included contact of wild geese with cattle or feed, poultry manure spread on connecting properties, signs of rodents in cattle housing or feed storage areas, the number of mature cows in the herd, percent change in the number of mature cows during the year and having calves born in a building rather than outdoors.

Additional risk factors other researchers identified are presence of cats, purchase of manure, feeding colostrum from own dam, non-season calving pattern, unrestricted grazing of lactating cows and a high average mowing percentage of pasture.

Ultimately the goal is to lower pathogens in the system. Certain possibilities of this include lowering the serotypes, killing them off, supporting the immune system of your herd and rapidly removing feces in the barn. Large herd size and intensive management may provide an environment conducive to salmonella shedding and chronic dairy herd infection. Once one part of the herd is infected, spread of salmonella bacteria occurs much more rapidly, especially to those with lowered immune status. The best proactive approach a producer can do to prevent the complications of salmonellosis is to keep animals comfortable and healthy.

The presence of multi-drug-resistant salmonella in dairy calves emphasizes the need for alternative, nonantimicrobial intervention strategies. Several years ago, calves in the Northeast with S. dublin presented symptoms of pneumonia and septicemia rather than the primarily diarrheal syndrome.

In a U.S. national survey of dairy operations with 30 or more milking cows, fecal samples from 6,800 preweaned dairy heifer calves on 1,063 operations were tested for salmonella. Of the fecal samples, 145 (2.1 percent) from 79 (7.4 percent) farms tested positive for salmonella.

Medicated milk replacer and hay fed to calves aged from 24 hours old until weaning were associated with a reduced risk of salmonella sheddings, as was calving in an individual animal area within a building. Water sampled from troughs used by weaned calves on California dairies showed salmonella present on four of 48 dairies (4/82 water samples) in the fall and on eight of 37 of the same dairies (8/83 water samples) in the summer.

Primary risk factors associated with increased incidence of salmonella in water offered to dairy calves were a continuous water tank filling method compared to an “on-demand” valve procedure and a water pH greater than 8.

The intestinal tract contains over 400 species of bacteria that compete for food and attachment sites. At birth, the intestine contains no bacteria. Lactobacillus bacteria normally begin to grow and occupy the intestine first. They generally help the calf avoid salmonella infections. Unfortunately, many of the other bacteria in the intestine are more susceptible to antibiotics than salmonella. Antibiotic treatment can actually promote the growth of salmonella by reducing the numbers of competing bacteria in the intestine.

Supplemental bacterial direct-fed microbials (DFM) can reduce the growth of undesirable bacteria by making organic acids that lower intestinal pH and the oxidation/reduction potential.

Bacterial DFM may also make antibiotics and other compounds that reduce pathogen growth. Beneficial bacterial DFM may have a faster rate of digestion and compete for food better than pathogens. Lactobacillus bacteria have been known to change the bile of the intestine so that it inhibits the growth of pathogens. Lactobacillus bacteria have also been found to reduce the level of intestinal amines, which can irritate the lining of the intestinal tract and cause diarrhea.

Problems with intake may also affect the balance of intestinal bacteria. Maintaining good dry matter intake using a balanced ration with adequate effective fiber should help control salmonella.

For pathogens like salmonella it is important for them to attach to the intestinal wall in order to survive, proliferate and do their damage. There is an interaction between the acidic mucopolysaccharide on the outer wall of the bacterial cells and the mucopolysaccharide layer of the intestinal cells. Bacterial fibrils enhance attachment. Bacterial DFM can compete for these attachment sites in the intestine.

Mannan oligosaccharides are fragments of cell wall from Saccharomyces cerevisiae (yeast) consisting mostly of phosphorylated glucomannans. Mannan is a sugar that is recognized by certain bacteria. Salmonella, E. coli and Vibrio cholerae all attach to the intestine via mannose-specific lectins (proteins or glycoproteins) on their cell walls. But when MOS is added to the diet, lectins are tricked into attaching to it rather than to carbohydrates on intestinal villi.

When mannan is in the form of an oligosaccharide, pathogens cannot use it to grow. Many intestinal pathogens specifically attach to mannan oligosaccharides and can be taken out of the intestine and excreted in the feces in this way rather than attaching to the intestinal wall to do damage. Researchers have found that the three-dimensional structure of the lipopolysaccharide of salmonella and organisms is critical in determining how well human mannose-binding lectin will attach to them.

One way that the mannose-binding lectins of humans and animals help against bacterial and viral infections is in a manner separate from the immune response. In humans it is believed that once mannose-binding lectin is bound to a microorganism, a complement system is activated separate from an antibody effect via two serine proteases (MASP-1 and MASP-2). The mannose-binding lectin may also promote phagocytosis of bacteria and viruses. They bind onto microorganisms with their C-terminal carbohydrate recognition domains and work with phagocytic cells via their N-terminal domains. This mode of action is especially important in young animals that do not possess a fully developed immune system.

Dairy producers and veterinarians have made progress in controlling salmonella infections through improved management, better nutrition and advanced biosecurity measures taken on the farm. The use of feed additives such as Lactobacillus acidophilus and mannan oligosaccharides show promise as a natural way to fight the organism. Antimicrobial drugs have been of limited help, and more research is needed to develop improved vaccines against salmonella. PD

References omitted but are available upon request at editor@progressivedairy.com

Randy Cragoe
Cragoe Consulting Services