Michaela Christina große Austing
Investigations on the occurence of Salmonella infections in pig farms
In the first part of this thesis the aim was to create a check list to identify the specific Salmonella infection sources and factors for the Salmonella perpetuation such as animal purchase, animal flow, management, feeding, watering, cleaning and disinfection, critical contacts (biosecurity) and pest control. This check list is thought to be universally usable in pig finishing farms for a Salmonella specific weak point analysis.
The following questions were examined: Where is a potential risk for the introduction and dissemination of Salmonella? (= analysis of Salmonella-specific critical points in pig finishing farms). How big is the risk for the occurrence of Salmonella estimated by the presence of individual risk factors on the basis of the own study and the literature?
Each of the participating farms (the closed system A with a breeding and a multiplying herd, a nursery and 6 finishing farms, the closed system B with a multiplying and a finishing farm, the breeding herd C and the finishing farm h) was visited and the farm was analysed with a check list, which was to be tested. Additionally, environmental and fecal random samples were taken and cultured in the lab of the Field Station for Epidemiology of the University of Veterinary Medicine Hanover. The culturing of the material was to verify the theoretical identified risk areas.
To revise the “check list to assess the Salmonella risk in pig finishing farms” used for the own studies the literature was searched for risk factors which are associated with a high Salmonella prevalence. From the results of the own studies, the evaluation of the literature and from exising check lists which were created by other study groups, the final check list and the points which allow a classification into a high, medium or low Salmonella risk were established.
In the second part of this thesis follow-up studies in the two closed systems were carried out to quantify the Salmonella occurrence and the Salmonella dynamics in pig farms.
The following questions should be answered: How is the dynamics of the Salmonella shedding in different animal groups? How is the development oft the antibody titers parallel to that? How good is the comparability between the serological and bacteriological results?
For this, different animal groups at the finishing farms of the closed system A were periodically bacteriologically examined. At slaughter, meat juice and blood samples were taken from 10% of the pig carcasses for a serological examination. In the closed system B two study groups with 20 marked animals each were sampled serologically and bacteriologically from weaning until slaughtering.
Additionally, the Salmonella Typhimurium live vaccine SALMOPORC® was tested in the closed system B. Two vaccinated study groups with 20 marked animals each were sampled from weaning until the slaughtering to answer the question: How is the dynamics of the Salmonella shedding and the antibody titers in animals which are vaccinated with the Salmonella Typhimurium live vaccine SALMOPORC®?
By culturing 266 environmental samples, factors which may be responsible for the circulation of Salmonella in the herd and the perpetuation of Salmonella infections could be identified.
The detection of Salmonella was successful in 3 dust samples, 3 samples of the ventilation system, 3 feed samples, 1 water sample, 2 rodents, 2 samples of rodent feces, 4 samples of flies, 1 sample of bird feces, 1 insect sample and a sample taken from a room for weighing growing gilts.
The dynamics of the Salmonella shedding in the different finishing groups of the closed system A showed great variations over the time and great differences in comparison of the different farms and the different finishing groups.
The comparison of the bacteriological and serological findings of the finishing groups showed partly big differences.
The follow-up examinations of the study groups 1 and 2 of the closed system B showed that the piglets immediately after weaning had low antibody titers. A lot of animals got infected in the nursery, showed fecal excretion and reacted positively in the ELISA at the end of the growing phase. In the finshing period, some animals excreted Salmonella, too. A lot of animals had their maximum of antibody concentration during this time period. At slaughtering, the antibody titers of some animals decreased below the cut-off.
The examination of the vaccinated animals (study groups 3 and 4) showed that a lot of animals excreted despite their immunization the field strain and developed already in the growing or later in the finshing period antibody titers above the cut-off. The number of Salmonella-positive animals in study group 4 was substantially lower than in the other three groups. Here, the vaccination, but also the improvement of the hygiene measures might have resulted in the reduction of Salmonella.
106 (92,1%) of the isolated Salmonella strains were identified as S. Typhimurium using the Kauffmann-White-scheme. Lysotype S. Typhimurium DT 104 dominated, followed by S.
Typhimuium DT 193, the Zoosal oral vaccination strain DT 009 and S. Typhimurium DT 120. Only a few S. Derby and S. Subspezies I. were isolated.
39 of the Salmonella isolates were examined for their resistance patterns and showed in 100%
resistance against Erythromycin, Tylosin, Lincomycin, Penicillin G, Oxacillin and Spectinomycin. Five of the S. Typhimurium DT 193 isolates showed resistance to 11 antimicrobials.
Altogether, the results of this study confirm the thesis of several working groups that in principle each pig farm has its own specific Salmonella dynamics and that the analysis of the farm specific Salmonella dynamics is indispensable for the establishment and implementation of targeted intervention measures.