Effect of waste milk pasteurization on fecal shedding of Salmonella in preweaned calves

Authors: Edrington, Thomas; GARCIA BUITRAGO, JOSE - New Mexico State University; HAGEVOORT, GERRIT - New Mexico State University; LONERAGAN, GUY - Texas Tech University; Harhay, Dayna; Callaway, Todd; Anderson, Robin; Nisbet, David

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2018
Publication Date: 10/1/2018
Citation: Edrington, T.S., Garcia Buitrago, J.A., Hagevoort, G.R., Loneragan, G.H., Harhay, D.M., Callaway, T.R., Anderson, R.C., Nisbet, D.J. 2018. Effect of waste milk pasteurization on fecal shedding of Salmonella in preweaned calves. Journal of Dairy Science. 101(10):9266-9274. https://doi.org/10.3168/jds.2018-14668.
DOI: https://doi.org/10.3168/jds.2018-14668

Interpretive Summary: Dairy calves are often fed non-saleable waste milk that has not been pasteurized and it has been hypothesized that this unpasteurized milk may be an important source contributing to high carriage of Salmonella in these calves. Accordingly, we conducted a study to determine if pasteurization of non-saleable waste milk influences fecal Salmonella concentrations in milkfed dairy calves. In this study, we collected fecal samples from 128 calves fed pasteurized waste milk and from 83 calves fed non-pasteurized waste milk. We found that overall, 69% of the fecal samples were culture positive for Salmonella and there was no statistically significant difference in amounts of Salmonella recovered from calves fed pasteurized or nonpasteurized waste milk. Seventeen different types of Salmonella were identified from those recovered with the majority being Salmonella types named Montevideo and Anatum. Of the lesser abundant Salmonella types, we found that the types named Typhimurium, Muenchen, and Derby were significantly more abundant, by at least 74%, in the calves fed the pasteurized waste milk than in calves fed the non-pasteurized waste milk. Conversely, we found that Salmonella types named Newport, Bredeny, and Muenster were significantly less abundant, by at least 56%, in the calves fed the pasteurized waste milk than in calves fed the non-pasteurized waste milk. The majority of all Salmonella isolated were susceptible to all of the antibiotics tested in this study; however, 38 individual Salmonella isolates were resistant to 8 to 9 antibiotics, and 1 exhibited resistance to 11 antimicrobials. These results demonstrate that pasteurization of waste milk did not influence overall fecal shedding of Salmonella in dairy calves but did appear to influence the type of Salmonella that was shed. This research provides important information to help dairy farmers better understand how Salmonella infects their dairy calves and how they may ultimately be able to prevent their infection.

Technical Abstract: To determine if pasteurization of non-saleable waste milk influences fecal Salmonella concentrations, prevalence, or antimicrobial susceptibility and serotype of cultured isolates, 211 Holstein dairy calves were housed on a single commercial dairy in the southwestern United States and randomly allotted to be fed either pasteurized (PWM; n = 128 calves) or nonpasteurized waste milk (NPWM; n = 83 calves). Animals were fed waste milk twice daily until weaning at approximately two months of age. Fecal samples were collected via rectal palpation or from freshly voided, undisturbed fecal pats, weekly during the first four weeks of the animal’s life and then again at weaning. Eight total collections were made and 1118 fecal samples cultured for Salmonella. One isolate from each culture positive fecal sample was preserved for antimicrobial susceptibility screening and serotyping. Sixty-nine percent of the fecal samples were culture positive for Salmonella with no difference (P > 0.10) due to treatment (67.7 and 69% Salmonella positive for PWM and NPWM treatments, respectively). Few fecal samples (178/1117; 15.9%) contained Salmonella concentrations above the LOD (~ 1 CFU/g feces) with concentrations ranging from 1.0 to 6.46 CFU (log10)/g of feces. Concentration was not affected by treatment (P > 0.10). Seventeen different serotypes were identified, the majority of which were S. Montevideo and Anatum. A greater (P < 0.05) percentage of Typhimurium (87 versus 13%), Muenchen (88 versus 12%), and Derby (91 versus 9%) were recovered from calves fed PWM compared to NPWM fed calves. Conversely, Newport (12.5 versus 86%), Bredeny (22.2 versus 77.8%), and Muenster (12.5 versus 87.5%) were lower (P < 0.05) in PWM compared to NPWM treatments. The majority (66.7%) of isolates were susceptible to all of the antibiotics examined. Thirty-eight isolates were resistant to 8 or 9 antibiotics, and 1 exhibited resistance to 11 antimicrobials. All MDR isolates with the MDR-AmpC pattern of resistance were recovered from calves in the PWM treatment and the majority (92%) were identified as Typhimurium. Results suggest that milk-borne Salmonella is not an important vector of transmission in dairy neonates, nor does pasteurization of waste milk influence fecal shedding of this pathogen. Waste milk pasteurization does appear to influence serotype prevalence, the exact mechanisms of which are unknown.