Research published in the September Journal of Dairy Science reported farms that raised heifers off-site have a higher risk of multi-drug resistant Salmonella. Washington State researchers visited 59 commercial dairies seven times over 15 to 21 months to collect fecal samples. Salmonella species were identified and tested for antibiotic resistance. Records from a state database also were collected to provide a history of disease caused by Salmonella on each farm.
In 46 percent of the herds tested, no new strains of Salmonella were found during the study. In the remaining 54 percent of herds, one to eight new strains of Salmonella were identified. Strains were considered “new” to a herd if they had not appeared over the previous three years. Investigators found increased risk for new multidrug resistant Salmonella strains in herds that raised heifers off-site or had disease caused by Salmonella in the past three years. Risk also grew as herd size increased in 100-animal units. Herds that raised heifers off-farm were 2.3 times more likely to contract new Salmonella strains than herds raising heifers on-site.
Purchasing infected animals is the primary route of Salmonella transmission between herds, and 49 percent of farms studied used custom heifer rearing. While these heifers were not technically purchased, they were comingled with heifers from several source farms. Growers need to be aware of this risk and should attempt to reduce Salmonella infection and transmission as much as possible on their operations.
Salmonella spreads by animals ingesting bacteria from feces. Therefore, prevent fecal contamination of feed and water. Rodents, birds and cats carry Salmonella and must be kept out of feed and water. Pasteurize waste milk before feeding to calves, and clean calf housing between every calf. Finally, encourage clients to keep maternity areas clean to limit infection of newborns.