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Salmonellosis

Salmonella infections are a serious cause of diarrhea in young calves. Salmonella can cause disease in cattle at all ages and are a health threat to humans and other species of animals that come into contact with cows or calves shedding organisms. Transmission occurs primarily through fecal contamination and can include everyday calving-season tools like esophageal feeders and calving chains.

Salmonella, like most infectious diarrheal agents, disrupt the balance of fluid moving into and out of the gut. The net result: excess fluid buildup in the intestine and resultant diarrhea, which in the newborn calf quickly causes dehydration and loss of life-sustaining electrolytes. Salmonella frequently invade the bloodstream and become generalized, causing damage to a number of organs including the heart, brain and skeletal system. Sudden deaths are not uncommon. Affected calves are typically lethargic and do not nurse. Fever, although variable, may persist for up to a week. Fecal consistency varies between watery to pasty with mucus, fibrin and blood. Severity of clinical signs is a play between immune status of the newborn, the dose of infection and virulence of the particular salmonella species involved. Because salmonellosis poses a danger to farm families and other animal species, producers should involve their veterinarian early, particularly in scour outbreaks where both cows and calves are involved, when there are sudden, unexplained deaths or if scouring calves are exhibiting diarrhea with large amounts of mucus and blood. Calves with elevated temperatures and exhibiting diarrhea containing mucus, fibrin and blood are classic salmonellosis candidates.

Diagnosis of salmonellosis is based on isolation of bacteria from the feces of clinically affected animals. Post-mortem lesions in calves dying of salmonellosis are quite characteristic. In the face of an outbreak, samples are often collected from a number of calves because salmonella can be isolated from calves showing no clinical signs. Special media are used to isolate salmonella in diagnostic labs. To further characterize the strain of salmonella involved, suspect colonies are subject to a series of biochemical and serological tests.

Two common salmonella species are associated with infections in cattle: Salmonella enteritica serovar Typhimurium (S Typhimurium) and Salmonella enterica serovar Dublin (S Dublin). S Typhimurium is commonly associated with outbreaks of infections in calves, especially dairy calves, less than two months of age. S Dublin is more often linked to disease in older calves and adult cattle. S Dublin tends to be more invasive and can be associated with brain and joint infections. Following ingestion, salmonella gain entry into the body after entering white blood cells

associated with the tonsils and wall of the intestine. The ability to survive within white blood cells — normally considered part of the body’s defence mechanism — enhances salmonella’s capacity to cause disease.

Treatment

Fluid replacement therapy is critical in treating all cases of diarrhea in calves. Salmonellosis is no exception. Some species of salmonella e. g. S Typhimurium DT 104 can be highly resistant to antimicrobials and, as a result, makes the use of antibiotics in treating salmonellosis controversial. Because salmonella infections in calves frequently become generalized aggressive treatment with antimicrobials early in the course of infections is recommended by many veterinarians. Non-steroid anti-inflammatory like flunixin (Banamine) are often included in treatment regimes.

Control and prevention basics

Infected calves can shed salmonella in feces, urine, saliva, and nasal secretions, contaminating everything they touch and everything that touches them (hands, esophageal feeders, nipples). A scouring calf with salmonellosis sheds millions of bacteria per gram of feces. Salmonella survive in a damp, cool environment for months.

Control and prevention of salmonellosis is similar to the control and prevention of other infectious causes of diarrhea in calves. The difference being: salmonella are serious human pathogens. The adaptation of salmonella as a pathogen in many species including humans and the potential they persist in a wide variety of locales including trucks, sale yards and a full gamut of livestock operations calls for rigorous attention to basic biosecurity principles.

A few important ones: In that some cows are chronic carriers, animals that recover from known bouts of salmonellosis should be culled (slaughter).

DO NOT buy auction mart specials to replace dead calves. The auction mart orphan, stressed and colostrum deprived has been the cause of many outbreaks of salmonellosis during calving season.

Sanitize anything that contacts the mouth of a calf (bottle nipples, esophageal feeders, pill guns, hands). Establish cleaning and disinfection protocols for family and staff, especially during calving season and post them where everyone sees them. Your veterinarian can assist with this task. Remember thorough cleaning is the first item on any disinfection protocol. Removing all organic matter (feces, blood, milk, saliva) is critical because organic matter protects infectious agents and interferes with the action of disinfectants. Choose the right disinfectant. Delay and minimize the infectious dose that the calf is exposed to. Minimize exposure dose by minimizing density of susceptible calves. Work with Mother Nature when possible. Green grass and sunshine are powerful barriers to infection.

Move cows and heifers to separate calving area several weeks before calving. Cows shedding organisms will contaminate winter feeding and bedding grounds. Heifers have poorer colostrum and require more supervision during calving.

If scours develop in a group, leave the affected group in place and turn out new pairs on to new pasture or clean calving grounds. Remember: during salmonellosis outbreaks the number of infected calves that appear normal yet shed salmonella outnumber visibly sick calves. Sick calves may be just the tip of the iceberg.

Maximize the calf’s natural resistance and acquired immunity. Ensure calves receive colostrum within two hours of birth. Colostral antibodies cross the calf’s gut wall into the bloodstream where they become an important component of the calf’s immune system. BE CLEAN! Reduce stress.

Maintain proper nutrition and body condition of the dam during the critical third trimester of pregnancy.

Ron Clarke is a veterinarian who writes from Stony Plain, Alta.

About the author

Columnist

Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).

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