A.A. Dijkhuizen

Economic analysis of animal diseases and their control

Abstract Animal Health Economics is a relatively new discipline, which is progressively developing a solid framework of concepts, procedures, and data to support the decision-making process in optimizing animal health management. Research in this field primarily deals with three interrelated aspects: (1) quantifying the financial effects of animal disease, (2) developing methods for optimizing decisions when individual animals, herds or populations are affected, and (3) determining the costs and benefits of disease control measures. In the paper the four most common economic modelling techniques (i.e. partial budgeting, cost-benefit analysis, decision analysis, and systems simulation) are described and applied on three levels of veterinary decision making: the animal, herd, and national level. Outcomes so far are summarized, and shortcomings indicated and discussed. The importance of a close link between economics and epidemiology is stressed for future development, as well as the need and possibilities for an international exchange of models and procedures.

An epidemiological and economic simulation model to evaluate the spread and control of infectious bovine rhinotracheitis in the Netherlands

Bovine herpesvirus type I (BHV1), causing infectious bovine rhinotracheitis (IBR), was introduced in the Netherlands in 1971. In 1993, about 42% of the dairy cows had antibodies against BHV1. In the future, stricter requirements are anticipated regarding the health status of exported breeding cows and material. To support policymakers in their decisions on IBR eradication, a simulation model was developed in which the epidemiological and economic consequences of various control strategies were evaluated. This paper describes the model and provides an overview of some important outcomes. In the model, dairy herds were classified into different disease states based on (1) the reproduction ratio of the disease (R, defined as the number of secondary cases caused by one infectious animal) (2) the within-herd prevalence, within each value of R and (3) the expected number of infectious animals in an infectious herd within each prevalence range. The dynamic transition probability of a herd going from one state to another per week depends on direct contacts between animals, and other contacts such as transmission through fomites, indirect transmission through other species, airborne transmission and minor disease-specific routes such as venereal or iatrogenic transmission. Five control strategies, including both a voluntary vaccination program and a compulsory vaccination program for all dairy herds were evaluated. A voluntary vaccination program with 50% participation is not expected to lead to eradication of IBR. It appears that compulsory vaccination would be necessary to reach an IBR-free status.

Risk factors for bovine respiratory disease in dairy youngstock in The Netherlands: the perception of experts

Abstract This paper describes a study aimed at quantification of expert opinion on risk factors for clinical bovine respiratory disease (BRD) in dairy youngstock in The Netherlands. For this purpose, a panel of 21 experts working in the field of BRD was selected. Total expert consultation consisted of five different rounds and included four rounds that comprised questionnaires held by mail and a 1-day workshop (last round). During the expert consultation different elicitation methods were used, such as the Delphi procedure and Adapted Conjoint Analysis (ACA). The most important risk factor for, respectively, mild and severe pneumonia in dairy calves aged 0–3 months was perceived to be (poor) air circulation and purchase of cattle. The latter risk factor was also considered as having the highest impact on the incidence of severe outbreak cases in dairy youngstock aged 3–6 months, whereas a previous case of BRD was considered to be the most important risk factor for mild outbreak cases. Outbreaks (both mild and severe) in dairy youngstock aged 6–24 months were perceived to be influenced most by air circulation.

Eliciting the relative importance of risk factors concerning contagious animal diseases using conjoint analysis: a preliminary survey report

Abstract Conjoint analysis is a technique well known in marketing research to elicit consumer preferences and opinions. This paper describes the results of an experiment which explores the potential application of conjoint analysis in the field of veterinary epidemiology and economics. In this experiment, the method of conjoint analysis was used to elicit the opinion of experts about the relative importance of risk factors concerning contagious animal diseases. Diseases studied were: African Swine Fever (ASF), Classical Swine Fever (CSF), Foot-and-Mouth Disease (FMD), Swine Vesicular Disease (SVD), Newcastle Disease (NCD) and Avian Influenza (AI). Risk factors included were import of livestock, import of animal products, feeding of swill, tourists, returning livestock trucks and air. The conjoint analysis technique was used to draw up a questionnaire which was handed out during the 7th ISVEE held at Nairobi, Kenya, from 15 to 19 August 1994. According to the experts approached, the factors ‘import of livestock’ and ‘import of animal products’ were the major sources of risk for all diseases. For ASF, CSF and FMD, the risk factor ‘swill feeding’ ranked third. For FMD and the two poultry diseases NCD and AI, only the risk factor ‘air’ was important. Overall conclusion was that conjoint analysis could be a useful method for eliciting the opinion of experts about risk factors concerning contagious animal diseases. In further research, special attention should be given to the selection of experts and the presentation of the conjoint questions.

Sharing risks in agriculture : principles and empirical results

The risk environment of farmers is changing. For example, price and production risks are increasing and governments increasingly encourage agriculture to find private market solutions for catastrophic risks like floods and epidemic diseases. We studied risk management strategies like insurance in which risks are shared with others to find out whether such strategies provide opportunities for farmers to deal with the new risks with which agriculture is confronted. We concluded, on both theoretical and empirical grounds, that risk-sharing strategies do provide such opportunities. From a theoretical perspective, because risk-sharing tools are in principle advantageous to both individual farmers and society as a whole, and from an empirical perspective, because farmers already perceive risk-sharing, especially insurance, as an important strategy to manage risks. The empirical results are based on a questionnaire survey among Dutch livestock farmers. Areas are identified for further research, amongst other things, with respect to risk-sharing strategies for price risks and epidemic livestock disease risks.

Risk attitude and decision making in contagious disease control

Abstract Accurate control of contagious animal diseases is of major concern for most countries. Basic and advanced decision rules are presented and applied, to show the impact of various risk attitudes of decision makers in determining what control strategy to choose, taking Foot-and-Mouth disease control in the Netherlands as an example. The choice appears to vary considerably among the decision rules (i.e. risk attitudes). Eventually, it is up to the decision maker to decide what rule is the most appropriate. Insight into the potential consequences of the various alternatives may contribute towards a more thoughtful approach in this respect.

Effects of bovine respiratory disease on the productivity of dairy heifers quantified by experts

Abstract The aim of the current study was to obtain expert data on the effects on productivity (EPs) associated with bovine respiratory disease (BRD) in dairy heifers. Expert knowledge on the EPs of BRD was elicited because a complete insight into these effects was not available from the literature. The experts’ assessments of the EPs were quantified, applying the computerised ELI technique, by means of subjective probability density functions (PDFs). For each EP, the individual experts’ PDFs were aggregated, hereby weighting the experts according to their expertise, to obtain a single weighted distribution per parameter. Results indicated that mortality following severe pneumonia in heifers

A knowledge documentation methodology for knowledge-based system development : an example in animal health management

Knowledge acquisition is one of the critical activities in developing a knowledge-based system. It includes on the one hand knowledge elicitation from different sources such as domain experts, books, maps and real-world observations, and on the other hand, a process of analysing, structuring and recording knowledge defined as knowledge documentation. Many methods have been developed to elicit knowledge, but not so many techniques are available for knowledge documentation. Those published often do not address all relevant aspects of the documentation process, or do not document all types of knowledge, for example, experts possess declarative and procedural knowledge. For constructing a knowledge-based system in the field of animal health management a documentation methodology has been developed and is reported in this article. The methodology was based on, among other things, the CommonKADS technique. It includes three subsequent phases: (1) documenting concepts and facts in hierarchies, (2) documenting separate inferences which integrate knowledge documented in hierarchies, and (3) documenting the strategy or sequence of the inferences to be made. The method supports the full pathway of the documentation process and addresses both declarative and procedural knowledge. Also, the method provides a quick insight into knowledge of a knowledge source (e.g. experts) and comprehensible transcripts for the expert. The latter facilitates the process of knowledge verification.

Simulation modelling of BHV1-control programme at national level, with special attention to sensitivity analysis

In this paper, the framework and basic results of the simulation model InterIBR-endemic are presented. This model was developed to support policy makers during the compulsory eradication programme for bovine herpesvirus type 1 (BHV1), that was implemented in The Netherlands in May 1998. The model closely interacted with a BHV1 monitoring programme, also related to the eradication campaign. The main objective of this study was to identify gaps in knowledge on BHV1 relevant for the eradication programme. For this, a detailed sensitivity analysis was performed for 31 model parameters. Simulation of the Dutch BHV1 eradication programme resulted in a median period of 334 weeks to reach a cow-level prevalence of 5% in the dairy cattle population, with median costs of EUR 106 million. Uncertainty of parameters for local spread and reactivation of BHV1 had most impact on both the period and costs of the simulated eradication programme. The uncertainty of the yearly reactivation rate of latently infected animals affected the costs by EUR 43 million. These factors should, therefore, have priority in further research.

Zovex, a knowledge-integrated computer system to support health management on pig farms

Abstract This paper describes the outline, knowledge acquisition and possible use of a knowledge-based system (KBS), called Zovex, for herd-health management support on growing and fattening pig farms. Zovex provides farm advisors with knowledge about the interaction between disease problems in a pig herd, and environmental and managerial factors on the farm influencing manifestation of disease. The first possible use of Zovex is that it can serve as an advisory tool in disease problem-solving. For that the system consists of (i) a health module triggered by the identified herd-health and production problem(s), (ii) a farm layout module containing data about the pig compartment identification and layout, and (iii) four risk factor assessment modules to analyse the presence or absence of disease-associated factors. The risk factor assessment modules include knowledge about disease and infection management, hygiene management, housing management and climate management. The output of Zovex is a list of risk factors present on the farm, and recommendations as to which risk factors are considered for interventions and how they should be changed. In addition to the problem-solving possibilities, Zovex can also be used as an advisory tool in preventive screening to identify problems as early as possible. Within this tool, user selected subsets of hygiene, climate or housing management risk factors are analysed. The type of output is similar to the problem tool of Zovex.