Salmonella is not at all a new challenge for dairy operations. And, the number of dairies it affects is growing. Even if you’ve never had a severe clinical outbreak in your herd, it still could be robbing performance from your cows, and dollars from your bottom line. And, its effects can span beyond the farm gate, affecting dairy workers’ health and, potentially, the human food supply.

 

Infection occurs when a susceptible animal ingests the bacteria. For dairy cattle, this often can be  through feed or water which has been contaminated with feces from other animals shedding the organism. An environmental reservoir is frequently a source of salmonella, as these environments

allow the gram negative bacterium to not only survive, but rapidly multiply. Other sources of infection may be rodents, birds, flies, feral cats, dogs raccoons and even people (though rarely). The principal route of infection is fecal-oral. Saliva, nasal secretions, colostrum and milk also can be the source of organisms’ shedding.

 

Once a portion of a herd is infected, it can be extremely difficult to tell which cows are shedding the

bacteria. “Salmonella is often found in the intestines of normal cows,” says Dr. Sheila McGuirk of the University of Wisconsin School of Veterinary Medicine.  “Salmonella is a pathogen that uses stress as an opportunity to manifest problems,” she adds.

 

“An outbreak of salmonella often comes with a sudden onset,” notes McGuirk, making it difficult to control before the damage is done. “Salmonella outbreaks cause an immediate production of endotoxins,” she says. “Often, even the most severe clinical signs of salmonella are a result of these

endotoxin reactions which then can take a cow down quickly.”  For the less mature calf, the combination of a sudden on-set and extreme endotoxin reaction is often lethal – before the manager even knows what hit them.

 

But, what about the subclinical effects caused by salmonella? If noclinical outbreaks are witnessed, is it safe to assume your herd is clean of salmonella? Not at all! “Several case studies lead us to believe that the subclinical infection rate of salmonella is significant,” McGuirk recently told an audience of dairy

producers in Wisconsin. “Studies conducted by my industry colleagues have shown that nine out of 20 free stall dairies had a positive isolate of salmonella, with S. Meleagridis being the most common,” she added.

 

In another 2004 study, data from 131 herds in 4 different states revealed 92.7 percent of the dairies tested positive for salmonella isolates.1 A Minnesota dairy case study conducted during SRP®  technology vaccine development, focused on salmonella fecal shedding control in a herd with no known signs or history of clinical salmonella. The objective of the study was to show any benefit in a “normal” herd. Preliminary fecal testing for subclinical shedding of salmonella identified that 50 percent of fresh cows in this herd were shedding either S. Anatum, S. Uganda or S. Melagridis.

 

In this study, cows were vaccinated at dry-off and boostered four weeks later. Cows were randomly selected, with an equal number of cows representing a control group. The results of this study demonstrated a derived benefit from the reduction of subclinical infections in that the average daily milk production from SRP-vaccinated cows in their next lactation was significantly higher than their herd mate control group. The somatic cell counts for these vaccinated animals also were lower than their contemporaries, but not statistically different.

 

In a pre-launch field study conducted in Colorado to demonstrate the safety of Salmonella Newport Bacterial Extract, results also suggest derived benefits from the control of clinical and subclinical salmonellosis. Similar to original research results when this technology was first introduced for turkey production, vaccination within an infected herd showed significantreduction in the presence of  salmonella.

 

In fact, within 3 weeks, the percent of animals testing positive dropped from animals. Two-hundred and forty days post-vaccination, salmonella shedding in this herd was confirmed to be less than one percent (0.6%). Initial testing showed the presence of several serogroups of salmonella in addition to S. Newport, and shedding decreased in all serogroups. “Though this study was conducted for the purpose of confirming the safety of the vaccine, milk production during the trial may suggest additional benefits to a dairy operation,” notes Dr. Travis Thayer, Technical Services Veterinarian for AgriLabs.

 

Results of the 240 day post-vaccination evaluation showed that cows vaccinated during the dry period averaged significantly more milk (305d MEM) than their non-vaccinated herd mates. The impact on

milk production may be a side benefit from the control of salmonellosis, clinical or subclinical. “While this is not something that will ever be a label claim for the product, it is an interesting observation that can have value for the dairyman.” Thayer adds. “While we cannot conclude that the use of a Salmonella vaccine like SRP will directly increase milk production, the results strongly suggest that a correlation between controlling Salmonella – even in subclinical or undetected herd status/conditions can lead to a healthier, more productive herd,” says McGuirk.