April 14 2010 01:41 PM
animal care and health

By Robert B. Moeller Jr., D.V.M., John Adaska D.V.M., and Patricia Blanchard D.B.M.
The authors are in the California Animal Health and Food Safety Laboratory, University of California, Tulare.

Salmonella infections continue to be a problem in both calf raising operations and dairy herds. Infections with these organisms can range from asymptomatic to severe intestinal and systemic disease.

Salmonella strains that are responsible for most infections in cattle, other animal species, and man are identified as a single Salmonella species called Salmonella enterica subspecies enterica. The various strains of Salmonella enterica subspecies enterica further are subtyped into individual serogroups based on various surface markers (called antigens) identified on the bacterial cell wall. The most important serogroups in cattle are serogroups B, C2, D1, and E. These organisms then are further identified by additional cell wall markers which allow your regional veterinary laboratory to name the bacteria as certain serotypes, that is, Salmonella Typhimurium, Salmonella Newport, or Salmonella Dublin.

Salmonella infections affect cattle of all ages. Serious illness most often is seen in newborns and young calves and in cows around calving. In both cows and calves, the most common clinical signs are diarrhea and fever. The diarrhea usually is watery to mucoid and may contain intermixed fibrin and blood. The feces often have a foul odor.

Watch fresh cows . . .
In cows, infections are most common in those that have calved within 10 days. However, there have been severe herd outbreaks involving all ages and stages of lactation. In addition to diarrhea, affected cows may have high fevers and drop in milk. Calves and cows can become depressed and dehydrated if not treated promptly. Cows rarely die, but the loss of milk can be significant. Most infections in cows involve Salmonella Typhimurium and Salmonella Newport.

Calves less than 30 days of age often are affected with Salmonella Typhimurium and Salmonella Newport. They often will lose tremendous amounts of body fluid due to the diarrhea. This loss of fluid and dehydration that results can cause severe metabolic problems which, if not treated quickly, may lead to death. In some cases, the Salmonella infection may become systemic leading to bacterial septicemia and death. Clinically, the diarrhea in Salmonella-infected calves often is difficult to distinguish from severe infections caused by coronavirus, cryptosporidia, and E. coli. Proper diagnostic workup of fecal samples from calves with diarrhea or the submission of sick or dead calves to your diagnostic lab is important in determining the cause.

Salmonella Dublin tends to affect older calves (30 to 90 days). However, in central California, we have seen infections in calves as young as 10 days. Infected calves may develop severe enteritis with foul-smelling diarrhea with fibrin and sometimes blood. Mild enteric infections without diarrhea are common with Salmonella Dublin since it is commonly associated with septicemia.

Calves often have high fevers and become dehydrated and depressed. If the diarrhea and dehydration is severe enough and the calf is not given supportive fluid therapy, it can die. Often, Salmonella Dublin infections lead to a severe bacterial septicemia involving the lungs, liver, and spleen. These can occur with or without diarrhea.

Calves with a Salmonella Dublin septicemia usually develop high fevers, pneumonia-like signs, and a moist cough. Often calves are found dead with no observed clinical signs. On rare occasions, Salmonella Dublin septicemias can cause thrombi to form in blood vessels of the ears, tail, and feet leading to dry gangrene and eventually loss of the affected areas.

Tough to prevent . . .
Prevention of Salmonella infections often is difficult since many animals in our herds are infected with these bacteria and intermittently shed the bacteria. The primary prevention method is to reduce exposure to the bacteria in susceptible animals. Good sanitary practices are a key.

In cows, keeping those recently fresh separated from sick ones will reduce exposure. Fresh cows and close-ups often shed Salmonella in their feces. Keeping the maternity area clean and free of manure can greatly aid in the prevention of an infection in susceptible cows.

Water troughs are another common source. They should be cleaned often. In a Salmonella outbreak, the daily cleaning and disinfecting of water troughs can help prevent further infections. Pools of stagnant water also are potential sources of infection. Draining and drying these low spots and preventing cattle from drinking this water (as well as lagoon flush water) also are important.

In studies performed on California dairies, both rodent and wild birds are found to carry various serovars of Salmonella, but these strains usually are not the strains found in cows. However, it still is a good idea to prevent birds and rodents from entering feed storage areas and to institute a good rodent control program.

People working in the hospital barn should never go to other areas of the dairy (particularly the calving pens and calf-raising areas) without first changing or disinfecting their boots, changing clothes, and washing hands and arms.

Salmonella infections in calves can start with contaminated milk. Feeding unpasteurized milk is always risky. This particularly is true for milk fed from the hospital cows or recently fresh cows. Monitor pasteurizers to ensure that they reach proper temperatures and times. Dairies using batch pasteurizers need to ensure the foam on top of the milk also is heated to the desired temperature to kill all bacteria. Plate-type pasteurizers need to be checked to ensure that they are heating milk properly. Proper cleaning and maintenance of plates are critical to ensure that residues do not build up which can decrease the temperature of milk passing through the pasteurizer and provide sites for bacterial colonization and contamination of the pasteurized milk.

Once milk is pasteurized by either method, it must be cooled quickly and properly stored (at 40°F) for later use or fed immediately to the calves. Rapid cooling of the pasteurized milk and the prevention of further bacterial contamination prior to feeding to the calves will help to ensure that the calves will not become infected. You should not allow colostrum to set out at room temperature for extended periods before being fed. Workers should always care for the youngest animals first before moving to the next older group. Once older ones are cared for, workers should never go back to younger animals unless they have thoroughly cleaned their boots, changed coveralls, and washed their hands and arms. Thorough cleaning of hutches between calves and the use of a good-quality disinfectant also is critical.

Treatment of cows for Salmonella usually involves oral fluid replacement therapy to replace the electrolytes and fluids lost due to diarrhea. Antibiotic therapy often is not necessary since most cows will recover. If antibiotic therapy is to be initiated, then you should first identify which approved antibiotics the Salmonella is sensitive to. Remember, antibiotics not only kill the Salmonella in the intestines but also kill beneficial bacteria in both the rumen and intestine. The loss of beneficial bacteria can lead to other complications.

In young calves, treatment needs to be aggressive. Newborns often have less fluid reserve than older cattle and can die quickly from dehydration and metabolic acidosis. Fluid replacement therapy either by oral supplementation or intravenous injection of electrolyte solutions must be pursued aggressively. Treatment with nonsteroidal inflammatories is important in making the calf feel better and promoting appetite. Use antibiotic therapy with caution. Knowing which antibiotics the bacteria is sensitive to always is important. Like in cows, use of antibiotics in calves can lead to other complications due to the death of normal beneficial bacterial flora. Excessive antibiotic use often can lead to fungal infections of the rumen and abomasum.

In calves with septicemia, you should start initial aggressive antibiotic treatment as soon as the calf develops clinical signs. Consequently, treatment protocols should be developed with your veterinarian and followed correctly.

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