EAST SYRACUSE, NY — Salmonella Dublin can devastate dairy herds, which is why the disease dominated entire sessions at the recent Calf & Heifer Congress hosted by Cornell University Cooperative Extension Northwest New York Dairy, Livestock & Field Crops Team and PRO-DAIRY.
Salmonella Dublin fit the theme “Rising Above the Challenges” quite well. Presenter Belinda S. Thompson, DVM with Veterinary Support Services Animal Health Diagnostic Center at Cornell’s College of Veterinary Medicine, shared with the 100-plus attendees why they should care about the disease.
She described Salmonella Dublin as “an insidious disease” since it is easily spread through silent carrier animals as well as sick individuals. The disease has developed resistance to multiple antibiotics and can make calves especially sick, as well as kill them.
“It’s very frustrating for calf caretakers,” Thompson added.
Since it’s zoonotic, the infection can transmit to people via infected excretions of sick cattle, or by consuming contaminated foods or raw milk.
This specific strain was recognized in New York State in 2006. In 2012, a bulk tank prevalence study confirmed that out of 5,245 total samples collected from 4,896 herds, 44 positive herds were detected with antibodies in milk, indicating exposure in the herd. That’s .90 percent.
Two years later, USDA sampling indicated 8 percent of dairies tested had Salmonella Dublin in a single bulk tank sample. Among those tested, 39.2 percent of dairies of 500-plus cows had the disease; 2.1 percent of dairies of 100-499 cows tested positive and 1 percent of dairies with 30-99 cows had Salmonella Dublin.
National Animal Health Monitoring System studies in 2014 showed through samples on bulk tanks that prevalence in the West was highest at 52.1 percent, followed by the Midwest (4.4 percent) and the East (0.6 percent). But Thompson warned that rates of salmonella Dublin have been on the rise for the past several years.
Lack of information on the disease may represent part of the reason why it has been steadily spreading.
Thompson said Salmonella Dublin is a different strain of Salmonella than what most producers and even veterinarians have experienced in their herds.
“Typically, it looks like sudden onset pneumonia in calves as its most common presentation,” Thompson said.
Usually, calves are one week to eight months old. Especially in calves this young, the disease bears a high death rate. Some calves exhibit just a high fever and die. Others experience seizures along with the fever. The animals may develop diarrhea, especially just before death.
Although calves in hutches can experience Salmonella Dublin, it’s most often seen among calves in group pens or where hutches are close together.
“Some calves get infected without getting sick,” Thompson said. “Some calves just get a fever and recover with or without treatment. Some calves get very, very sick but appear to respond to antibiotic treatment. Many calves die despite aggressive antibiotic and other treatment.”
Salmonella Dublin’s unpredictability makes it frustrating for producers to treat. At times, it’s also more difficult to spot among older animals, which typically don’t show illness.
“If they do, abortion of pregnant animals is one important presentation,” Thompson said.
Ill cows may also appear to have coliform mastitis, but without the actual mastitis. Adult cattle with Salmonella Dublin rarely exhibit diarrhea. Animals infected while young and treated with an antibiotic are more likely to become a carrier.
All of these factors have helped Salmonella Dublin “become solidly entrenched in New York State herds,” Thompson said.
Many producers introduce the disease to their farms through purchasing infected animals, heifers returning from off-site heifer raisers, returning show animals, embryo recipient dams, offspring of embryo recipient dams, and manure, milk or colostrum from other farms.
Thompson said as with buying a used car, farmers need more information on the “used cows” that they purchased, “like a ‘cow fax’ on the animals,” she quipped.
The disease infects cattle in the tonsils, blood stream, major organs, lymph nodes and in bodily fluid. Healthy carrier animals may harbor the disease in the lymph nodes and intermittently in bodily fluids and feces.
Animals often spread the disease though feeding utensils, shared bottle nipples, unpasteurized waste milk, colostrum, manure-contaminated feed, shared water, contaminated bedding and anything else that comes in contact with infected bodily fluids.
Salmonella Dublin has shown sensitivity to three of the 20 antibiotics available: entrofloxacin, gentamycin and trimethoprim/sulphamethoxazole.
“Even with antibiotics, bacteria can overwhelm the patient when they have already spread to all tissues,” Thompson said. “This is also true in human sepsis cases. Treated animals that survive may be and often are permanently stunted and/or unproductive.”
While antibiotics can help treat individual animals, overall it can lead to the development of more antibiotic resistance.
Instead, Thompson promotes prevention to control Salmonella Dublin.
“This is a real risk to all farms,” she said.
She wants farmers to put more effort into keeping their farms clean, including not allowing old milk and feed to sit out. While rodents have been proven to spread other strains of Salmonella, Dublin may or may not be spread this way.
Thompson wants farmers and veterinarians to scrub their boots and change their coveralls between farms to prevent spreading illness.
“The swine and poultry industry have been doing this a long time,” Thompson said.
In her second presentation that followed, Thompson said reducing risk is well worth it. A farm with which she’s familiar spent $50,000 on controlling risk factors, which they felt was money well spent since they were losing $200,000 annually from disease losses.
In addition to economic losses from treating and losing animals, operators also must think of animal welfare, lawsuit liability, and public relations. By following good animal care procedures; operators can raise healthier, more productive animals, too.
Wearing disposable gloves to treat animals — and washing between animals anyway — can help reduce spread of illness. Producers should also carefully monitor animals for signs of illness and quickly isolate sick individuals.
“If you get a sick calf, get it out,” Thompson said. “You may save the rest.”
While stanchions limited cow movement and decreased cow comfort, Thompson said they did tend to curtail illness because they limited how much cows mingled, unlike free stall barns. The take-away lesson is that sick animals should be separated from well ones.
Thompson said the maternity pen should separate dams and their calves from the herd, not simply place a fence between them. Pooling colostrum, skipping colostrum or feeding replacement colostrum places calves at higher risk.
Flushing out manure spreads infected feces more than using ally scrapers. It’s all about understanding how the disease spreads, and limiting the contact animals have with contaminated animals and their bodily fluids.