Serologische und epidemiologische Untersuchungen zur Identifikation von Risikofaktoren für die Ausbreitung von Salmonellen in Aufzuchtbeständen für Jungsauen

The aim of this study on gilt breeding herds was to determine seasonal variations in the Salmonella seroprevalence and to discover production-specific risk factors for a high seroprevalence. A total of 13.511 results from 11 nucleus herds, 19 supplier herds and 46 gilt breeding herds were available for the statistical analysis. Blood samples were taken monthly from 2001 until 2003 from gilts five and six months of age. Included in the statistical analysis of risk factors were only those 52 herds from which at least 60 samples per year and 10 per quarter were available. Further examinations were based on data supplied by the breeding company and on results obtained from a questionnaire and subsequent visual examination of the pigs in the herds and their environment. Herd-specific factors were evaluated statistically in connection with the serologic results to determine seasonal variations and identify risk factors. Six different kinds of classification were tested between herds with “low” and “high” Salmonella seroprevalences. Overall seroprevances of Salmonella were low in the herds of this study (0-18 %). All 52 herds will be classified in category 1 (< 20 %) according to the QS grading system. The statistical analysis of risk factors shows a significantly higher seroprevalence during the winter quarters (October until December; January until March). Higher seroprevalences are found in herds with higher pig density, and the impact of this factor is statistically significant (p< 0,10) in all kinds of classification. Higher seroprevalences are also detected in five of the six kinds of classification among PRRSV-free herds. However, statistical analysis of all other factors reveals an impact only in individual kinds of classification or not at all; these parameters can therefore not be considered to be risk factors with absolute certainty. Seroprevalences in the population examined here are low in comparison to those of other studies in Germany. For the intepretation of these low seroprevalences it must be pointed out that the examined pig herds belong to a single breeding company, which has a very strong commitment to good management and hygiene procedures, and it is likely that the lack of or low level of salmonella exposition is a consequence of such procedures. Therefore low exposition to the infective agent is probable in the herds examined here. Since no evidence was found for many risk factors known from other studies, it can be assumed that those factors are more likely to have an impact on the spread of salmonella in herds with a higher salmonella exposition. In the classification of herds the clear seasonal dependence of the Salmonella seroprevalences should be taken into consideration within the scope of monitoring programs. Scoring of herds is only meaningful after regular sampling for at least one year. Further investigation of the factors that lead to higher Salmonella seroprevalence in winter is necessary. From other investigations pig density is also known to be a risk factor for higher seroprevalence. The marked impact of this factor, which was proven in this population with a low seroprevalence, suggests that pig density is a particularly sensitive factor. Further investigations are necessary to determine if the absence of PRRSV really does constitute a risk of higher Salmonella seroprevalences in a herd. In previous work any such impact of this factor was mentioned; in fact, experimental and epidemiological investigations have reported that this factor has an opposite effect on Salmonella prevalence – or none at all.