Salmonella is hard to avoid
A research project was set up to to determine if pasteurization of nonsaleable waste milk influences fecal Salmonella concentrations and prevalence.
All the data came from one large dairy in southwest USA. They collected 1,117 fecal samples and found that 69% of the sample positive for Salmonella.
The percentage positive was the same for calves fed either non-pasteurized nonsaleable milk and pasteurized nonsaleable milk.
Nonsaleable milk samples were collected and cultured (6 of each pasteurized and non-pasteurized). Only one non-pasteurize sample was culture positive for Salmonella.
The authors speculate that Salmonella in the dairy environment was a plausible vector of transmission since the milk regardless of treatment was unlikely to the source of infection.
I conclude that we must depend on control strategies other than pasteurizing our nonsaleable milk to lower our Salmonella infection rates.
A case study of a Salmonella outbreak at a calf-raising facility highlighted two prevention:control stratgies.
(1) Monitor passive transfer immunity - in this case study calves with blood serum total protein levels less than 5.0 had twice the mortality rate as those with levels of 5.0 and higher (16% compared to 8%).
(2) "Do not depend on footbaths to kill pathogens, especially Salmonella. It was cultured from multiple footbaths on this raising unit during the outbreak."They found that "providing separate boots, clothing, and rubber gloves to be worn in each calf barn and adhering to traffic flow patterns that do not allow cross-contamination of multiple areas will likely be more effective for managing the risk associated with epidemic salmonellosis."
References: Edrington, T. S. and Others "Effect of waste milk pasteurization on fecal shedding of Salmonella in preweaned calves." Journal of Dairy Science 101:9266-9274 October 2018.
Gardner, C.E. and Others "Case Report - Management of an outbreak of salmonellosis on a commercial calf raising unit." The Bovine Practitioner 38:2 pp 147-154. June 2004.