Dissemination of Salmonella enterica subsp. enterica serovar Typhimurium var. Copenhagen clonal types through Contract Heifer Raising Operation
Posted: December 4, 2005
In June of 1998, a heifer raising operation in Pennsylvania with recurrent problems associated with calf mortality sought the assistance of the Field Investigation Group at Pennsylvania State University to address the issue.
Beginning of August of 1998, the veterinarians attending the heifer raising operation and 18 dairy herds that received heifers from the heifer raising operation were asked to submit samples (fecal and tissue samples) for bacteriological analysis from all clinical cases suggestive of Salmonellosis. Between September 1998 and October 2000, samples from of 324 calves, heifers and lactating cattle from the heifer raising operation and 11 dairy herds were cultured for Salmonella using the protocol followed by Pennsylvania Animal Diagnostic Laboratory for isolation and identification of Salmonella. Salmonella isolates were serotyped at the National Veterinary Services Laboratory, Ames, Iowa.
A total of 62 Salmonella isolates belonging to 6 serotypes including S. Typhimurium, S. Typhimurium var Copenhagen, S. Muenchen, S. Newport, S. Heidelberg, and S. Montevideo were isolated. Salmonella Typhimurium var Cophenhagen (STC) accounted for 42 of the 62 (68%) Salmonella isolates.
These isolates have been previously isolated from calves, heifers and lactating cows in Pennsylvania. Statistical analysis showed that on the dairy farm, the likelihood of isolating STC from a sick heifer was 2.6 fold higher than from sick calves. With regard to STC, the likelihood of isolating STC from calves on the heifer raising operation was 5.3 fold higher than from heifers, while on the dairy farm STC was more likely (2.3 fold higher) to be isolated from heifers than from calves.
Transition of animals from one environment to another (e.g., dairy farm to heifer raising operation and vice-versa), change in nutrition (protein and energy content), and interaction with other animals (access to stall, and water and feed troughs) in the cohort could result in a cascade of events that could induce stress making the animal more susceptible to infectious diseases.
These sets of complex interactions could perhaps explain the higher Salmonella infection rates of calves that were transferred to the heifer raising operation and in heifers that returned to their dairy herds. An indepth genetic analysis based on DNA fingerprinting revealed that STC isolates shared similar genetic profiles.
Contract heifer raising requires meticulous planning and implementation of rigorous biosecurity practices. Biosecurity deals with management practices that protect the herd from entry of new diseases and minimize the spread and/or adverse effects of diseases in the herd. A contract heifer raising operation acquires calves from several farms that are co-mingled. This is the single most important risk factor for introduction of new diseases on the premises.
More importantly, the organisms may leave the premise, healthy heifers serving as vehicles. Biosecurity is one of the major issues facing professional heifer growers who have multiple clients. Most contract raising operations include biosecurity practices to address brucellosis, persistent bovine viral diarrhea disease and Johne’s disease. Based on the findings of our study it is felt biosecurity practices focused on prevention and control of enteric pathogens yet remain to be addressed adequately.
In summary, Salmonella Typhimurium var. Copenhagen isolates from a heifer raising operation and 11 dairy herds that contracted their calves to the heifer raising operation were examined for their characteristics. Results of the study showed that the heifer raising operation could serve as a clearing house of S. Typhimurium var Copenhagen and perhaps other Salmonella serotypes.Bhushan Jayarao and David Wolfgang, Veterinary Science Extension