Project Summary

Examination of Waste Milk Pasteurization on Salmonella Prevalence in Dairy Cattle

Principle Investigator(s):
Tom S. Edrington, Todd R. Callaway, and David J. Nisbet
U.S. Department of Agriculture, Agricultural Research Service
Completion Date:
May 2008



Ruminants, including dairy cattle, serve as an important reservoir for Salmonella and have been implicated in cases of human salmonellosis. Research conducted by our laboratory has found the prevalence of mature dairy cattle shedding Salmonella in their feces varies greatly, but can be as high a 100%. However, as dairy cattle are most often asymptomatic and sporadic carriers/shedders of Salmonella, identification of Salmonella-positive animals cannot be accomplished visually. Therefore, strategies for “on-farm” control of Salmonella will have to incorporate all of the animals within a farm or target specific groups or ages of cattle.   

While targeting a large group of animals in this manner will likely be the most effective means of lowering Salmonella prevalence, it may also prove to be the most expensive.   

Recent research conducted by our laboratory and funded by America’s Beef Producers, sought to determine the prevalence of multi drug resistant (MDR) Salmonella and to determine which if any age or production groups on the farm may be more likely to harbor MDR Salmonella. While this research did identify groups with a higher MDR Salmonella prevalence (hutch calves, sick/fresh cows), one of the most interesting results of this research involved the feeding of waste milk.   

Waste milk (milk from medicated cows) is often saved and used as a cheap feed source for calves, reducing dependence on milk replacer or saleable whole milk. However, it is unknown if this management practice facilitates the transfer of pathogenic or antimicrobial resistant bacteria.   

Pasteurization of the waste milk is employed by some facilities but the degree of effectiveness or the effects on mediators of resistance transfer are unknown. In the aforementioned research, we made two sample collections (October 2005 and March 2006) and found Salmonella prevalence (overall and MDR) decreased substantially in the March collection, not only in the calves, but also in lactating cows and animals in the sick pen. In talking to the farm manager, we learned that the dairy had started pasteurizing the waste milk approximately three months prior to the March collection resulting in a substantial decrease in cases of calf salmonellosis and an improvement in overall calf health. While our data only suggests pasteurization of waste milk may reduce Salmonella prevalence on the farm, the implications of this potential finding certainly warrants further examination. 

The stated objectives for this work were: 

  • Determine prevalence of Salmonella and MDR Salmonella in dairy calves (1 to 60 d of age) fed pasteurized or non-pasteurized waste milk. 
  • Determine if waste-milk pasteurization influences Salmonella prevalence in older animals (6, 12, and 24 month old heifers) and overall farm prevalence (to include lactating and dry cows), including multi drug-resistant (MDR) Salmonella
  • Examine waste milk (pasteurized and non-pasteurized) for: 
    • Salmonella 
    • Antibiotic residues 
    • Generic microbial population 
  • Evaluate and compare antimicrobial efficacy of antibiotic residues in pasteurized and non-pasteurized waste milk (if residues present). 
  • Compare commensal bacterial populations and gastrointestinal ecology of calves fed pasteurized and non-pasteurized waste milk.

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