The first part of this work involved a small animal study which involved vaccinating six Friesian bull calves with either live attenuated Salmonella Dublin or Salmonella Typhimurium or a control antacid. However when challenged with infection, both the vaccinated and unvaccinated control animals showed a GIFN response. This showed a possible presence (or history) of Salmonella in the environment.
A sampling of a negative farm, where all animals tested negative for Salmonella, was now carried out. Again responses to both Salmonella Dublin and Salmonella Typhimurium were seen in some of the yearlings and in most of the milking cows. This implied the possibility of the existence of Salmonella in the environment or some natural immune responses.
An alternate controlled animal study was propose, however this could not be carried out due to time and financial constraints, and therefore a new objective had to be found.
Here six farms were selected who had recent history of either Salmonella Dublin (three famrs) or Salmonella Typhimurium (3 farms). On each visit samples were taken from various animals, the environment, then feed and local wildlife. These samples were tested for the presence of all Salmonella serotypes.
Farms with a recent history of Salmonella Dublin
Out of the positive Salmonella samples found, two of the three farms had a low proportion of Dublin serotypes in comparison to all the positive samples. In these farms, infection was mainly found in calves. In the third farm however, a majority of the positive Salmonella samples were Dublin. The other Salmonella serotypes present in each farm were primarily caused by wildlife.
Farms with a recent history of Salmonella Typhimurium
In all three farms, approximately 50% of all positive samples were caused by Salmonella Typhimurium, however on one of the farms, this fell to around 10% over the course of the visit.
Additional conclusions
Salmonella Typhimurium survived longer than Salmonella Dublin at ambient temperatures.
All strains survive for longer in dry conditions than in wet.
