Multi Criteria Decision Making to evaluate control strategies of contagious animal diseases.

The decision on which strategy to use in the control of contagious animal diseases involves complex trade-offs between multiple objectives. This paper describes a Multi Criteria Decision Making (MCDM) application to illustrate its potential support to policy makers in choosing the control strategy that best meets all of the conflicting interests. The presented application focused on the evaluation of alternative strategies to control Classical Swine Fever (CSF) epidemics within the European Union (EU) according to the preferences of the European Chief Veterinary Officers (CVO). The performed analysis was centred on the three high-level objectives of epidemiology, economics and social ethics. The appraised control alternatives consisted of the EU compulsory control strategy, a pre-emptive slaughter strategy, a protective vaccination strategy and a suppressive vaccination strategy. Using averaged preference weights of the elicited CVOs, the preference ranking of the control alternatives was determined for six EU regions. The obtained results emphasized the need for EU region-specific control. Individual CVOs differed in their views on the relative importance of the various (sub)criteria by which the performance of the alternatives were judged. Nevertheless, the individual rankings of the control alternatives within a region appeared surprisingly similar. Based on the results of the described application it was concluded that the structuring feature of the MCDM technique provides a suitable tool in assisting the complex decision making process of controlling contagious animal diseases.

Preferences of cost factors for mastitis management among Dutch dairy farmers using adaptive conjoint analysis.

Although many control practices to improve the mastitis situation on a farm and to reduce the economic losses of mastitis are available, the adoption rate and level of compliance of these measures are generally low. Implementing new measures involves costs, which can be divided into costs for the milking parlour and other issues. These costs were subdivided into long term investments, short term investments, labour, and change of routines. In traditional cost-benefit analyses all costs belonging to the different factors are set on a comparable monetary value. Although in an economic way this is correct, farmers may value some costs in a different way because of certain preferences, influencing the adoption rate of the mastitis reducing measures. The objectives of this study were to explore differences between preferences of cost factors according to Dutch dairy farmers, and to distinguish different groups of farmers accordingly. 136 farmers were questioned by adaptive conjoint analysis about their individual preferences. A large difference between these preferences was found. Taking individual preferences together, overall, long term investments in issues other than milking parlour were preferred most and changing routines in issues other than milking parlour were preferred least. The results of this study show that, given the large variation in the valuations, to improve the adoption rate of management measures it is important to take the preference of cost factors into account in advice given.

Field study on broiler eggs hatchability.

The aim of this research was to explore factors that are related with hatchability in the field. Data from 3 Dutch hatcheries for the years 2004, 2005, and 2006 were analyzed using a random regression model with the method of restricted maximum likelihood. In total, 24,234 batches of 724,750,444 eggs, originating from 511 breeder flocks, were included. Annually, 241,583,481 eggs were set on average, which is 37% of the total annual eggs set in the Netherlands. A significant difference in hatchability among eggs from different breeder flocks was found. Hatchability was significantly related with flock age, egg storage length, strain, feed company, season, year, as well as hatchery (P < 0.001). There was also significant interaction between flock age and age at first delivery, egg storage length at hatchery, strain, feed company, and season. Other 3-way interaction terms were also significant. The variation in hatchability was larger among the breeder farms than within breeder farms. The average estimated difference in hatchability among the hatcheries was 8%. The average estimated hatchability at 25 wk of age was 66%; it increased to 86% between 31 and 36 wk and decreased to 50% at 65 wk of age. On average, an extra day of storage until d 7 reduced hatchability by 0.2% and from d 7 to 14 by 0.5%. Eggs from older flocks were less sensitive to prolonged storage, whereas they were more sensitive to season. Hatchability was greater during late summer than during spring. The average estimated differences in hatchability among strains and feed companies of the breeder farms were 8 and 2%, respectively. Based on the relations found, optimization of hatchery results depends not only on good management at the hatchery but also on the hatching egg quality and therefore on the breeder farm management. It can be concluded that production data that are collected by the hatcheries can be used to adjust the management decisions at hatcheries as well as breeder farms.

The influence of cow factors on the incidence of clinical mastitis in dairy cows.

Many cow-specific risk factors for clinical mastitis (CM) are known. Other studies have analyzed these risk factors separately or only analyzed a limited number of risk factors simultaneously. The goal of this study was to determine the influence of cow factors on the incidence rate of CM (IRCM) with all cow factors in one multivariate model. Also, using a similar approach, the probability of whether a CM case is caused by gram-positive or gram-negative pathogens was calculated. Data were used from 274 Dutch dairy herds that recorded CM over an 18-mo period. The final dataset contained information on 28,137 lactations of 22,860 cows of different parities. In total 5,363 CM cases were recorded, but only 2,525 CM cases could be classified as gram-positive or gram-negative. The cow factors parity, lactation stage, season of the year, information on SCC from monthly test-day records, and CM history were included in the logistic regression analysis. Separate analyses were performed for heifers and multiparous cows in both the first month of lactation and from the second month of lactation onward. For investigating whether CM was caused by gram-positive or gram-negative pathogens, quarter position was included in the logistic regression analysis as well. The IRCM differed considerably among cows, ranging between 0.0002 and 0.0074 per cow-day at risk for specific cows depending on cow factors. In particular, previous CM cases, SCC in the previous month, and mean SCC in the previous lactation increased the IRCM in the current month of lactation. Results indicate that it is difficult to distinguish between gram-positive and gram-negative CM cases based on cow factors alone.

Towards flexible decision support in the control of animal epidemics.

Decision-making in the control of animal epidemics is a dynamic and flexible process. Facing uncertainties about the consequences of control options, flexible decision-making can avoid unnecessary control costs through learning and adjusting. While recognising the importance and complexity of decision-making, research has paid little attention to flexibility in deciding whether and when to use certain control options. The implicit assumption that control options are taken either immediately or never may lead to significant bias in selecting control strategies. This paper systematically analyses the elements in the decision-making process of animal epidemic control to illustrate the importance of flexibility. Also discussed are various ways of integrating flexibility into research on decision-making in animal epidemic control.

Cost-effectiveness of measures to prevent classical swine fever introduction into The Netherlands.

Recent history has demonstrated that classical swine fever (CSF) epidemics can incur high economic losses, especially for exporting countries that have densely populated pig areas and apply a strategy of non-vaccination, such as The Netherlands. Introduction of CSF virus (CSFV) remains a continuing threat to the pig production sector in The Netherlands. Reducing the annual probability of CSFV introduction (P(CSFV)) by preventive measures is therefore of utmost importance. The choice of preventive measures depends not only on the achieved reduction of the annual P(CSFV), but also on the expenditures required for implementing these measures. The objective of this study was to explore the cost-effectiveness of tactical measures aimed at the prevention of CSFV introduction into The Netherlands. For this purpose for each measure (i) model calculations were performed with a scenario tree model for CSFV introduction and (ii) its annual cost was estimated. The cost-effectiveness was then determined as the reduction of the annual P(CSFV) achieved by each preventive measure (DeltaP) divided by the annual cost of implementing that measure (DeltaC). The measures analysed reduce the P(CSFV) caused by import or export of pigs. Results showed that separation of national and international transport of pigs is the most cost-effective measure, especially when risk aversion is assumed. Although testing piglets and breeding pigs by a quick and reliable PCR also had a high cost-effectiveness ratio, this measure is not attractive due to the high cost per pig imported. Besides, implementing such a measure is not allowed under current EU law, as it is trade restrictive.

Stochastic efficiency analysis of bovine tuberculosis-surveillance programs in the Netherlands.

We constructed a stochastic bio-economic model to determine the optimal cost-efficient surveillance program for bovine tuberculosis. The surveillance programs differed in combinations of one or more detection methods and/or sampling frequency. Stochastic input variables in the epidemiological module described the dynamics of infection and the probability of detection. By means of an efficiency frontier, the trade-off between the expected cost and the epidemiological risk parameter relating to the outbreak size was evaluated. The surveillance scheme based on visual inspection of lesions on carcasses at slaughter was optimal given the current prevalence of the disease in the Netherlands if the objective was to minimise the expected costs. However, the efficient set also included two other schemes: slaughterhouse inspection in combination with GAMMA-interferon testing of blood samples and slaughterhouse inspection in combination with two-stage tuberculin testing. The choice ultimately will depend on the risk attitude of the decision-maker; a more-stringent surveillance scheme will be enforced if the expected outbreak size is to be constrained. In future scenarios, ELISA testing of bulk-tank milk in combination with the current slaughterhouse inspection procedure would outperform the surveillance scheme of solely slaughterhouse inspection if ELISA testing of bulk-tank milk becomes feasible.

Improving food safety within the dairy chain: an application of conjoint analysis.

This study determined the relative importance of attributes of food safety improvement in the production chain of fluid pasteurized milk. The chain was divided into 4 blocks: "feed" (compound feed production and its transport), "farm" (dairy farm), "dairy processing" (transport and processing of raw milk, delivery of pasteurized milk), and "consumer" (retailer/catering establishment and pasteurized milk consumption). The concept of food safety improvement focused on 2 main groups of hazards: chemical (antibiotics and dioxin) and microbiological (Salmonella, Escherichia coli, Mycobacterium paratuberculosis, and Staphylococcus aureus). Adaptive conjoint analysis was used to investigate food safety experts' perceptions of the attributes' importance. Preference data from individual experts (n = 24) on 101 attributes along the chain were collected in a computer-interactive mode. Experts perceived the attributes from the "feed" and "farm" blocks as being more vital for controlling the chemical hazards; whereas the attributes from the "farm" and "dairy processing" were considered more vital for controlling the microbiological hazards. For the chemical hazards, "identification of treated cows" and "quality assurance system of compound feed manufacturers" were considered the most important attributes. For the microbiological hazards, these were "manure supply source" and "action in salmonellosis and M. paratuberculosis cases". The rather high importance of attributes relating to quality assurance and traceability systems of the chain participants indicates that participants look for food safety assurance from the preceding participants. This information has substantial decision-making implications for private businesses along the chain and for the government regarding the food safety improvement of fluid pasteurized milk.

Sick leave analysis among self-employed Dutch farmers.

BACKGROUND: Agriculture is one of the most physically demanding and risky industries. Aim The objective of this study was to provide baseline data on the diagnoses, occurrence and duration of sick leave of self-employed Dutch farmers. METHOD: A database of 22 807 sick leave claims of 12 627 farmers during the period 1994-2001 was analysed. RESULTS: Most of the claims (61%) were for musculo-skeletal injuries and disorders. The mean cumulative incidence (CI) was 10.2 claims per year per 100 farmers and did not change over time. However, it varied per agricultural sector and per age category, being lowest in arable farming and in the youngest age category and highest in mushroom farming and in the oldest age category. The duration of sick leave depended both on diagnosis and age category: the slowest recovery from sick leave was seen in farmers with respiratory diseases and farmers in the oldest age category. CONCLUSION: The results make it easier to identify groups of farmers to be targeted to prevent sick leave. To reduce the occurrence of sick leave in agriculture, the strategy should be to prevent musculo-skeletal injuries and disorders. Furthermore, a sector-specific approach is recommended, so that preventive actions can be focused on working conditions-specifically on workload and work safety. Efforts to shorten the duration of sick leave will also be valuable to obtain a reduction of sick leave.

The risk of the introduction of classical swine fever virus at regional level in the European Union: a conceptual framework.

Recent classical swine fever (CSF) epidemics in the European Union (EU) have clearly shown that preventing the introduction of CSF virus (CSFV) deserves high priority. Insight into all the factors contributing to the risk of CSFV introduction is a prerequisite for deciding which preventive actions are cost-effective. The relations between virus introduction and spread, prevention and control, and economic losses have been described using the conceptual framework presented in this paper. A pathway diagram provides insight into all the pathways contributing to the likelihood of CSFV introduction (LVI_CSF) into regions of the EU. A qualitative assessment based on this pathway diagram shows that regions with high pig densities generally have a higher LVI_CSF, although this cannot be attributed to pig density only. The pathway diagram was also used to qualitatively assess the reduction in LVI_CSF achieved by restructuring the pig production sector. Especially integrated chains of industrialised pig farming reduce the LVI_CSF considerably, but are also difficult and costly to implement. Quantitative assessment of the LVI_CSF on the basis of the pathway diagram is needed to support the results of the qualitative assessments described.

A decision-tree to optimise control measures during the early stage of a foot-and-mouth disease epidemic.

A decision-tree was developed to support decision making on control measures during the first days after the declaration of an outbreak of foot-and-mouth disease (FMD). The objective of the tree was to minimise direct costs and export losses of FMD epidemics under several scenarios based on livestock and herd density in the outbreak region, the possibility of airborne spread, and the time between first infection and first detection. The starting point of the tree was an epidemiological model based on a deterministic susceptible-infectious-recovered approach. The effect of four control strategies on FMD dynamics was modelled. In addition to the standard control strategy of stamping out and culling of high-risk contact herds, strategies involving ring culling within 1 km of an infected herd, ring-vaccination within 1 km of an infected herd, and ring-vaccination within 3 km of an infected herd were assessed. An economic model converted outbreak and control effects of farming and processing operations into estimates of direct costs and export losses. Ring-vaccination is the economically optimal control strategy for densely populated livestock areas whereas ring culling is the economically optimal control strategy for sparsely populated livestock areas.