Economic and epidemiological evaluation of Salmonella control in Dutch dairy herds

Wageningen UR, Agricultural Economics Research Institute, P.O. Box 35, 6700 AA Wageningen, The Netherlands.
Preventive Veterinary Medicine (Impact Factor: 2.51). 03/2009; 89(1-2):1-7. DOI: 10.1016/j.prevetmed.2008.12.007
Source: PubMed

ABSTRACT This paper presents an analysis of a Salmonella control program for Dutch dairy herds. Salmonella control strategies were evaluated using a computer-based model consisting of an epidemiological module and an economics module. The epidemiological module is a state transition model of the infectivity of a herd, with the unit of analysis being the individual farm. The probability of a herd going from one state in the model to another state was derived from biological characteristics of Salmonella infections in dairy herds, and the presence or absence of risk factors. The economics module was based on partial budgeting. Control measures were modeled as influencing the risk factors. Amongst the measures considered were the prohibition of transporting potentially infectious animals and manure to farms, the culling of chronically infected animals, and herd management measures such as separate housing of groups of animal that differ in age. Alternative strategies, both compulsory and obligatory, were defined and evaluated concerning the reduction of prevalence of infected herds, the cost of a strategy, and cost-effectiveness. Results of the model suggested that a compulsory control strategy which included culling chronically infected animals and prohibiting the transport of potentially infected animals reduces the prevalence of Salmonella positive herds considerably, and was most cost-effective. Adding hygienic measures and a ban on the transport of animal manure further reduces prevalence, but only slightly, and with substantially more costs.

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    • "enterica serovar Dublin (Salmonella Dublin) is a bacterium that leads to compromised animal health and production losses in cattle herds worldwide (McDonough et al., 1999; Carrique- Mas et al., 2010). Therefore, several countries have initiated research and extended programs for screening and control of this infection in their cattle populations (Veling et al., 2002; Bergevoet et al., 2009; Lewerin et al., 2011). "
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    ABSTRACT: Salmonella Dublin is a bacterium that causes disease and production losses in cattle herds. In Denmark, a surveillance and control program was initiated in 2002 to monitor and reduce the prevalence of Salmonella Dublin. In dairy herds, the surveillance includes herd classification based on bulk tank milk measurements of antibodies directed against Salmonella Dublin at 3-mo intervals. In this study, an "alarm herd" concept, based on the dynamic progression of these repeated measurements, was formulated such that it contains predictive power for Salmonella Dublin herd classification change from "likely free of infection" to "likely infected" in the following quarter of the year, thus warning the farmer 3 mo earlier than the present system. The alarm herd concept was defined through aberrations from a stable development over time of antibody levels. For suitable parameter choices, alarm herd status was a positive predictor for Salmonella Dublin status change in dairy herds, in that alarm herds had a higher risk of changing status in the following quarter compared with nonalarm herds. This was despite the fact that both alarm and nonalarm herds had antibody levels that did not indicate the herds being "likely infected" according to the existing classification system in the present quarter. The alarm herd concept can be used as a new early warning element in the existing surveillance program. Additionally, to improve accuracy of herd classification, the alarm herd concept could be incorporated into a model including other known risk factors for change in herd classification. Furthermore, the model could be extended to other diseases monitored in similar ways.
    Journal of Dairy Science 10/2013; 96(12). DOI:10.3168/jds.2012-6478 · 2.55 Impact Factor
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    • "Previous simulation studies of Salmonella have focused on transmission parameters within the herd as well as introduction and persistence of the infection (Xiao et al., 2006; Nielsen et al., 2007; Lanzas et al., 2008; Chapagain et al., 2008). Bergevoet et al. (2009) investigated cost and cost-effectiveness compared to the reduction in herd level Salmonella prevalence of different national control strategies for Dutch cattle herds at national level. However, there were no estimations of losses associated with the disease at herd level in that study. "
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    ABSTRACT: Salmonella Dublin affects production and animal health in cattle herds. The objective of this study was to quantify the gross margin (GM) losses following introduction and spread of S. Dublin within dairy herds. The GM losses were estimated using an age-structured stochastic, mechanistic and dynamic simulation model. The model incorporated six age groups (neonatal, pre-weaned calves, weaned calves, growing heifers, breeding heifers and cows) and five infection stages (susceptible, acutely infected, carrier, super shedder and resistant). The effects of introducing one S. Dublin infectious heifer were estimated through 1000 simulation iterations for 12 scenarios. These 12 scenarios were combinations of three herd sizes (85, 200 and 400 cows) and four management levels (very good, good, poor and very poor). Input parameters for effects of S. Dublin on production and animal health were based on literature and calibrations to mimic real life observations. Mean annual GMs per cow stall were compared between herds experiencing within-herd spread of S. Dublin and non-infected reference herds over a 10-year period. The estimated GM losses were largest in the first year after infection, and increased with poorer management and herd size, e.g. average annual GM losses were estimated to 49 euros per stall for the first year after infection, and to 8 euros per stall annually averaged over the 10 years after herd infection for a 200 cow stall herd with very good management. In contrast, a 200 cow stall herd with very poor management lost on average 326 euros per stall during the first year, and 188 euros per stall annually averaged over the 10-year period following introduction of infection. The GM losses arose from both direct losses such as reduced milk yield, dead animals, treatment costs and abortions as well as indirect losses such as reduced income from sold heifers and calves, and lower milk yield of replacement animals. Through sensitivity analyses it was found that the assumptions about milk yield losses for cows in the resistant or carrier stages had the greatest influence on the estimated GM losses. This was more influential in the poorer management scenarios due to increased number of infected cows. The results can be used to inform dairy farmers of the benefits of preventing introduction and controlling spread of S. Dublin. Furthermore, they can be used in cost-benefit analyses of control actions for S. Dublin both at herd and sector level.
    Preventive Veterinary Medicine 04/2013; DOI:10.1016/j.prevetmed.2013.03.011 · 2.51 Impact Factor
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    • "enterica Dublin (S. Dublin) is a cause for concern in cattle industries across many countries (McDonough et al., 1999; Bergevoet et al., 2009; Carrique-Mas et al., 2010; Lewerin et al., 2011) because of the economic losses and welfare consequences such as high mortality, morbidity, abortions and a reduced milk yield (Richardson and Watson, 1971; Visser et al., 1997; Nielsen et al., 2010, 2012b). Furthermore, infrequent but serious human infections occur and are mainly attributed to the consumption of beef or unpasteurised milk products (Maguire et al., 1992; Helms et al., 2003). "
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    ABSTRACT: Salmonella Dublin infections reduce gross margins and compromise animal health and welfare in dairy cattle herds. Despite on-going control efforts in several countries the duration and risk factors of a persistent infection have been difficult to study due to a lack of suitable data. This study utilised the unique opportunity to extract systematically collected repeated bulk-tank milk antibody measurements from all the Danish dairy herds during a 10-year period to perform a time-to-event analysis of the factors that affect the duration of test-positivity and the hazards of recovery from S. Dublin at herd level.
    Preventive Veterinary Medicine 03/2013; 110(3-4). DOI:10.1016/j.prevetmed.2013.02.014 · 2.51 Impact Factor
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