Salmonella in Cattle

Livestock Update, May 2002

Dr. W. Dee Whittier, Extension Veterinarian, Cattle, VA-MD Regional College of Veterinary Medicine

Salmonella is a bacteria that causes disease in nearly all types of mammals. Its most common symptom is diarrhea but it can invade nearly any tissue in the body. It is of concern to cattlemen because it can cause disease and death in cattle. It is also a concern because it is one of the most important food borne diseases of humans with an estimated 1.3 million cases annually and 550 deaths.

Salmonella can be considered almost as a normal inhabitant of the cattle digestive tract. A 2000 feedlot study was done to assess the amount of Salmonella in large feedlots in the US. Fecal samples were collect from cattle pens and cultured for the bacteria. Overall 22.3 percent of pens sampled had at least one positive sample. Over half of all feedlots had at least one sample that was positive. While there are few cases of Salmonella in humans that are associated with beef this is due in large part to procedures in place during the slaughter and distribution of beef that prevent the Salmonella in the digestive tract and on the hair coat of cattle from contaminating beef.

The feedlot study of cattle Salmonella infections looked at seasonal patterns of isolation. Samples taken during the summer months (July through September) were three times as likely to be positive when compared with winter (January through March) samples. Spring samples had rates of Salmonella isolation that were more than double those of winter. The thought is that the bacteria multiply much more readily in feed and water supplies during the warm months.

Much of the Salmonella disease seen in Virginia beef cattle is seen in the spring and summer as well. The disease is seen as scours outbreaks in calve with more severe diarrhea and death loss than in typical scours outbreaks. Occasionally we see outbreaks in other ages of cattle as well. Herds of adult cows have been affected with 1% to 50% of the herd becoming infected. Severe diarrhea with some death loss is seen as well.

Factors that lead to Salmonella outbreaks in cattle are though to be related to three factors:

• The dose of Salmonella that cattle consume.
• The resistance levels of cattle
• The virulence or disease producing ability of the particular Salmonella strain to which cattle are exposed.

Since cattlemen can do little about the strain of Salmonella that is present on their farms preventing losses is a function of two factors:

1. Decreasing exposure to Salmonella. Biosecurity measures that decrease exposure are the major approach to exposure prevention. These include preventing manure contamination of feed and water, being very careful with new animal introductions, being sure feed sources are clean and isolating cattle that have disease.
2. Keeping cattle resistance high. This approach is key to preventing losses from many of the common cattle diseases. Approaches include adequate nutritional management, special are at stressful times (shipping, weaning, calving, etc), providing plenty of colostrum to newborn calves and preventing other diseases that can lower resistance.

The presence of Salmonella in cattle operations seems to be a fact of life in modern cattle operations. Losses from these bacteria and contamination of our food products need not be.

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