Over 2400 serotypes of Salmonella have been identified and many have been associated with foodborne illness. Salmonella spp. are ubiquitous in nature and they have been recovered from nearly all vertebrate including pigs, cattle, poultry (including eggs), turkeys, fin and shellfish. Investigators have demonstrated that pigs can harbor Salmonella spp. up to the time of slaughter. Information regarding the development and maintenance of a carrier state is limited and confined to experimental challenge. Currently, the most effective control of salmonellosis in pigs is rigorous sanitation and treatment of animals including prophylactic treatment with antibiotics. Studies regarding the rearing of pigs free of infectious diseases in an infected environment is limited and none is available concerning Salmonella in swine.

In 1988 Harris proposed that economically significant diseases could be eliminated without depopulation by placing the various stages of production on multiple isolated locations. He modified the medicated early weaning procedure developed by Alexander and others and found similar results if piglets were simply isolated from the source farm at weaning. Since that time, many producers throughout the swine industry have either modified old facilities or built new ones in either three isolated or multiple isolated site designs.

We developed a need to determine if pigs could be raised free of Salmonella for research purposes. Previously, laboratories have relied on using pigs that were caesarian derived and colostrum deprived (CDCD) or procuring pigs anticipating that they would be free of Salmonella spp. Use of CDCD pigs is very costly and investigators have indicated that pigs they procured at six weeks of age for use in experiments were not free of Salmonella spp. (Wood, personal communications).

For all trials, building access was limited and personnel routinely change coveralls and boots and wore gloves when in contact with the pigs. No medication was given to pigs prior to or after weaning. Samples were routinely collected from the pigs for bacteriologic culture to determine if Salmonella spp. were present. Samples included fecal specimens, and rectal, tonsil, and nasal swabs. Sows were also sampled.

If the pigs were negative for Salmonella spp. at six weeks of age, they were used in other experiments. Within each experiment, a control group, which was never challenged with live Salmonella spp., was monitored by bacteriologic examination to determine if Salmonella spp. were present. Control pigs were also necropsied on selected days and tissues were collected for bacteriology.

Farm A included trials 1 through 4. Forty-three gilts were procured and transported to isolation facilities at the National Animal Disease Center (NADC) to farrow. We weaned 285 pigs at 21 days of age and placed them in other isolation facilities. Fifty-nine pigs from trial 1 and seventy-one pigs from trial 4 remained free of Salmonella spp. at 6 weeks of age for use in other experiments. Nineteen pigs in trial 2 and 15 pigs in trial 3 became positive for Salmonella derby.

Farm B included trials 5 through 9. One hundred forty-two pigs were procured at 14 to 17 days of age, transported to NADC, and placed in isolation facilities. We were able to raise and maintain 68 pigs from trials 5 and 7-9 free of Salmonella spp. to 6 weeks of age for use in other experiments. During trial 6, which involved 74 pigs, 7 became positive for Salmonella mbandaka.

Farm C included trials 10 through 16. One hundred seventy-two pigs were procured at 10 to 14 days of age, transported to NADC, and placed in isolation facilities. We were able to raise and maintain all 172 pigs free of Salmonella spp. to 6 weeks of age for use in other experiments.

Sows were positive for Salmonella spp. for trials 1-3, 5, 6, and 9. Ages of control pigs remaining free of Salmonella spp. from all experiments are listed in Table 1. Only the homologous Salmonella spp. challenge isolate was recovered from pigs used in experiments suggesting that these pigs remained free of any heterologous Salmonella spp. Currently, our standard protocol for raising and maintaining pigs free of Salmonella for research use is as described for Farm C. These data suggest that by use of isolated weaning techniques, and within the detectable limits of bacterial culture, we were able to maintain pigs free of Salmonella spp. for experimental purposes. However, as observed for trials 2, 3, and 6, we expect that there will be occasions when this is not possible.

Regarding elimination of Salmonella spp. on the farm by use of isolated weaning techniques, we have surveyed four farms to determine the prevalence of Salmonella spp. Sample collection included fecal specimens, tonsil/nasal/rectal swabs, feed, dust and water.

Farm D was positive for S. choleraesuis var. kunzendorf, S. anatum, and S. derby. Farms E and F were negative for Salmonella spp. Farm G was positive for Salmonella spp. serogroup B and the isolates are currently being serotyped. The SC-54 Salmonella vaccine (Nobl Laboratories, Sioux City, IA) is currently in use on farms D, F and G.

We purchased thirty-eight pigs from farm D. Nineteen pigs were transported to NADC at 10 to 14 days of age. Nineteen pigs remained on the source farm and they were integrated with the rest of the herd. The SC-54 Salmonella vaccine was not used for either group of pigs and no medications were given.

To date, we have not recovered any Salmonella spp. from pigs at NADC or the source farm. Environmental samples are positive for Salmonella spp. on the source farm. We will continue to monitor pigs to market age.

Farm G will be included in an upcoming trial which will be conducted as described for farm D. Two additional source farms from out of state, one with a known S. choleraesuis var. kunzendorf problem and one with a known S. typhimurium problem, will also be included in upcoming trials. These trials will be conducted entirely on-site with separate isolation facilities for the control groups.

Alexander, T.J.L., Boon, K.T.G., Lysons, R.J., & Gush, A.F. (1980) Veterinary Record 106, 114.

Bean N.H. & Griffin P.M. (1990) Journal of Food Protection 53, 804.

Duhamel, G.E., Bernard, R.J., Fedorka-Cray, P.J., Erickson, E.D & Hygnstrom, S.E. (1992) Proceedings 12th International Symposium on New and Emerging Infectious Diseases, San Diego, p381.

Fitzsimmons, M. & Leman, A.D. (1991) Unpublished data, Swine Graphics, Webster City, IA.

Hammer, J.M. (1991) Proceedings Livestock Conservation Institute, Minneapolis, p151.

Harris, D.L. (1988a) Veterinary Record 123, 422.

Harris, D.L. (1988b) Proceedings United States Animal Health Association, Little Rock, p416.

Harris, D.L. (1990) Large Animal Veterinarian May/June, 10.

Harris, D.L. (1992) Proceedings Southeast Swine Practitioners Conference, Raleigh, p1.

Hunneman, W.A. & Oving, L. (1991) Veterinary Quarterly 13, 172.

Kampelmacher, E.H., Edel, W., Wuinee, P.A.M., & Jansen, L.M. (1969) Zbl. Veterinary Medicine 16, 717.

Katsube, Y., Tanaka, Y., & Imaizumi, K. (1973) Japan Journal of Veterinary Science 35, 25.

Keteran, K., Brown, J. & Shotts, E.B. Jr. (1982) American Journal of Veterinary Research 43, 706.

Laval, A., Morvan, H. Deperez, G., & Corbio, B. (1991) Rec Med Vet 167, 835.

Linton, A.H., Heard, T.W. Grimshaw, J.J, & Pollard, P. (1970) Research in Veterinary Science 11, 523.

McCapes R.H., Osburn, B.I., & Riemann, H. (1991) Journal of the American

Veterinary Medical Association 199, 875.

Pillen, J.D. (1991) Unpublished data, Sands Livestock Systems, Columbus, NE.

Samuel, J.L., O’Boyle, D.A., Mathers, W.J. & Frost, A.J. (1979) Research in Veterinary Science 28, 238.

Taylor, J. & McCoy J.H. (1969) Foodborne Infections and Intoxicants. New York, Academic Press. p3.

Wilcock, B.P. (1986) Disease of Swine. 6th ed. Ames, Iowa State University Press. p508.

Wilcock, B.P. & Schwartz, K.J. (1992) Diseases of Swine. 7th ed. Ames, Iowa State University Press.p.570.

Wood, R.L., Pospischil, A., & Rose, R. (1989) American Journal of Veterinary Research 50, 1015.

Wood, R.L. & Rose, R. (1992) American Journal of Veterinary Science 53, 653.

 

 

 

 

 

Age (weeks)

Sample 6 7 8 9 10 12 15 18 >31

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Swab/fecala 370b 45 38 23 21 15 11 10 2

Necropsyc 45 7 15 2 6 4 1 8 NDd

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a tonsil, nasal and rectal swabs were taken and include the pigs that were necropsied

b 280 pigs were challenged with Salmonella spp. for use in experiments, 45 pigs remained as controls

c a minimum of 14 tissues were collected and processed by bacteriologic culture to

determine if Salmonella spp. were present

d not determined, pigs are still alive