Management is Best Tactic to Stop Salmonella

Best management practices, along with good biosecurity, are the first steps in keeping this organism from taking hold in a herd.

Talk to any livestock operator – or veterinarian – who has dealt with a Salmonella outbreak, and you will quickly grasp the severity of this destructive bacteria.

Infected animals – most often newborn calves – usually develop fever and diarrhea which can frequently lead to death caused by dehydration and intestinal lesions. But even worse, research studies indicate the Salmonella organism can be shed by cattle for days, weeks, or a year or more. Specifically, cattle infected with the serotype Salmonella Dublin may shed for life with no clinical signs. Salmonella can also exist in manure and manure-amended soils if it is not properly composted.

With that kind of persistence, salmonellosis is a disease that demands livestock operators’ attention – to prevent it from spreading in their cattle herds, at feedlots, and into the human food supply.

Presently, the National Animal Health Monitoring System (NAHMS) pegs the prevalence of Salmonella-positive beef cow-calf operations in the U.S. at about 10%. NAHMS conducted surveys in 1997 and 2007-08 and found that number has remained steady.

NAHMS data collected from dairy operations indicate that Salmonella occurrence on U.S. dairies is increasing. NAHMS reports found that the percentage of Salmonella-positive dairy operations, based on individual culture of feces from healthy cows, has increased with each NAHMS dairy study, from 21.1% in 1996 to 39.7% in 2007. The percentage of Salmonella-positive cows on those operations also has increased, from 5.4% in 1996 to 13.7% in 2007.

What’s the best strategy for combating this killer?

Because many of the newly identified Salmonella strains are resistant to antibiotics, the most effective solution to this issue is management through biosecurity practices.

Helen Aceto, epidemiologist and biosecurity director at the University of Pennsylvania’s School of Veterinary Medicine, cites results from her research to support this. She collected data from sites that experienced outbreaks of antibiotic-resistant Salmonella Newport and found:

Farms that had average management practices had >50% mortality among at-risk animals that developed clinical signs.
Farms that had excellent management practices still had high morbidity among at-risk animals, but with much lower mortality.

She emphasizes, “Farms that implemented best management practices had animals that got sick from Salmonella, but none or very few died.”

Namely, biosecurity protocols are key to preventing Salmonella from establishing on site, says Aceto. Specifically, Salmonella are most commonly transmitted by fecal-oral contamination from livestock or by cattle ingesting contaminated feed. Rodents or birds may play a role in spreading contamination. Thus it is important to keep potentially infected animals or contaminated feed away from other livestock.

She lists cows and heifers that have recently calved, along with newborn calves, as the most at-risk for infection, and says it is critical to ensure biosecurity practices protect them.

Biosecurity basics

Biosecurity steps, Aceto recommends, include:

Removing any sick animals to a hospital pen as soon as they have been identified. In particular she says, “Do not allow contact – not even a shared waterer – with at-risk animals such as close-up or recently fresh cows.”
When bringing new animals into the herd, if at all possible keep new cattle separate from the main herd for a quarantine period of at least 14 to 21 days.

Despite these steps, Aceto cautions that some animals can be

asymptomatic carriers. She explains that while we do not yet fully understand the precise mechanisms of shedding recurrence, one possible scenario is that when an infected animal’s immune system is functioning at a high level, the bacteria can be warded off – but may remain inactive inside specific cells of the animal’s system. Then, when the animal is stressed, the bacteria can begin to multiply and spread into the lower intestine from where they can begin to be shed in the feces and potentially go on to infect other animals. With that said:

Utilize management to minimize stress on the herd – from proper nutrition and a good vaccination herd-health program to low-stress animal handling.
Minimize the risk of contaminated feed by purchasing quality feedstuffs from mills and suppliers with good biosecurity practices.
Once feed is on site, control bird and rodent access to the feed by enclosure if possible. Clean up feed spills immediately so birds and rodents are not attracted to the area.
Consider traffic patterns when mixing and delivering feed to limit the risk of fecal contamination.
Keep water sources clean.

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Staggering Salmonella Stats

More than 2,400 different serotypes of Salmonella have been identified. In recent years, the most dominant strains in livestock are two serotypes – Salmonella Typhimurium DT104 and Salmonella Newport – that are resistant to multiple antibiotics and both of which can be transmitted from livestock to people and vice versa.
A USDA Food Safety Inspection Service report indicates that DT104 appears to cause a higher morbidity and mortality rate among infected animals than other Salmonella serotypes. One UC-Davis study documented a calf mortality rate of 60% by 10 days of age during a DT104 outbreak that occurred in extremely hot weather.
A strain of Salmonella Newport termed Salmonella Newport MDR-AmpC is currently the third most frequently detected Salmonella serovar in the U.S. MDR-AmpC refers to the fact that this organism is multi-drug resistant and carries the AmpC gene which confers resistance to late-generation cephalosporin antibiotics such as cetiofur (i.e. Naxcel®, Excenel®). Salmonella Newport MDR-AmpC is typically resistant to at least nine of the 17 standard drugs used on the National Antimicrobial Resistance Monitoring System’s test panel, many of which are important to the treatment of enteric bacterial infections.
In a University of Pennsylvania lab study documenting the survival of Salmonella enteric serovar Newport in manure and manure-amended soils, it was found that the organisms persisted 184, 332, and 405 days in manure, manure-amended non-sterilized soil, and manure-amended sterilized soil, respectively. Helen Aceto notes that survival would be different in a real-world setting subject to the elements, but says survival is still likely to be prolonged under warm and damp conditions.

According to the Centers for Disease Control and Prevention (CDC), salmonellosis in humans causes an estimated 1.4 million cases of foodborne illness and more than 400 deaths annually in the United States.

Most persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most recover without treatment.

Consumers can help prevent salmonellosis through safer food preparation such as washing hands and surfaces often; avoiding cross-contamination of raw and cooked foods, especially meats; cooking foods to safe minimum internal temperatures; and promptly and properly refrigerating foods.