The calls all have a similar ring to them. "I perform DA surgeries on many farms, but, on this one farm, the animals tend to die. Why is that?"
John House, associate clinical professor of veterinary medicine at the Veterinary Teaching Hospital at the University of California-Davis, often fields calls from veterinarians when things don't go as expected. In the above scenario, and in many others like it, the culprit lurking in the background tends to be salmonella.
"It's an opportunistic pathogen," explains House. "When things get out of synch, such as when an animal is compromised, salmonella can strike." Once an outbreak starts, sick animals shed the organism, which multiplies the contamination in the environment and puts healthy animals at risk.
Salmonella commonly strikes in the hospital pen, fresh-cow pens and in calves. Producers often treat sick animals with antibiotics, but with salmonella, the animals don't necessarily get any better, says Craig Meadows, veterinarian in Turlock, Calif.
In animals showing clinical signs of salmonella, death losses can be as high as 20 percent to 50 percent, says Meadows. But, it doesn't have to be that way. Once producers learn what they are dealing with, they can limit the spread when an outbreak occurs, and even minimize the chance of another oubreak occurring.
Use these five steps to do just that.
1. Know the signs
In order to get a quick jump on salmonella, and limit its spread, you have to know the clinical signs, says George Barrington, assistant professor in large animal medicine at Washington State University. Depending on the age of the animal, its level of immunity and virulence of the salmonella strain, it will manifest itself in one of three ways: peracute septicemia, acute enteritis or chronic enteritis. The most common signs include diarrhea - often with blood or mucus in it, fever, depression, down animals, off feed, dehydration and bloodshot eyes.
Once you identify an animal with clinical signs, test to confirm which strain is present. Although 2,200 serotypes of salmonella exist, only about 10 commonly affect cattle, explains Barrington.
Fecal, blood and, tissue samples from dead animals can all be used to identify the strain. In farms where salmonella has struck before, oftentimes it is the same strain coming back to haunt you. However, most farms have several strains of salmonella lurking in the background. So, before you give any antibiotics, determine which serotype is present and what antibiotics it is sensitive to, stresses House.
2. Isolate animals with clinical signs
Immediately isolate all animals with clinical signs, says Meadows. If, for example, you have one cow with clinical signs in a fresh-cow group of 25, you need to remove and isolate that one animal. Consider all of the remaining animals in that group as "at risk" and quarantine them.
Research has shown that some cows shed salmonella without ever developing clinical signs. So quarantining the rest of the group is an important step. While quarantined, no new animals should enter the group, or leave the group. Watch for clinical signs, and if possible, take daily rectal temperatures, suggests Meadows. A sudden fever is one of the first warning signs that an animal is infected with salmonella.
Infected animals shed salmonella in their feces, urine, nasal secretions and saliva. The incubation period ranges from one to four days. So, if none of the other animals in that group develop clinical signs after four days, you can remove the quarantine.
With calves showing clinical signs, be sure to confine to an individual pen and do not allow to suckle other calves.
Isolation can be impractical in some herds. In those cases, treat the entire group as infected and take measures to prevent the spread of salmonella to other groups.
3. Prevent transmission
Once you have animals isolated, make sure your employees don't unknowingly transfer the pathogen to another group of animals, says Barrington. Use these guidelines:
- Care for and feed infected animals last. When done, employees should change coveralls, wash their hands with soap and water and scrub and disinfect boots.
- If you use a skid-steer to clean out pens in an infected area, clean and sanitize it before using in an uninfected animal area.
- Do not use the same tractor and loader to clean pens and handle feed. If you have to, disinfect equipment before using it to load feed.
- Do not allow sick animals to wander loose around the dairy.