Economic efficiency analysis of different strategies to control post-weaning multi-systemic wasting syndrome and porcine circovirus type 2 subclinical infection in 3-weekly batch system farms

Abstract

The study assessed the economic efficiency of different strategies for the control of post-weaning multi-systemic wasting syndrome (PMWS) and porcine circovirus type 2 subclinical infection (PCV2SI), which have a major economic impact on the pig farming industry worldwide. The control strategies investigated consisted on the combination of up to 5 different control measures. The control measures considered were: (1) PCV2 vaccination of piglets (vac); (2) ensuring age adjusted diet for growers (diets); (3) reduction of stocking density (stock); (4) improvement of biosecurity measures (bios); and (5) total depopulation and repopulation of the farm for the elimination of other major pathogens (DPRP). A model was developed to simulate 5 years production of a pig farm with a 3-weekly batch system and with 100 sows. A PMWS/PCV2SI disease and economic model, based on PMWS severity scores, was linked to the production model in order to assess disease losses. This PMWS severity scores depends on the combination post-weaning mortality, PMWS morbidity in younger pigs and proportion of PCV2 infected pigs observed on farms. The economic analysis investigated eleven different farm scenarios, depending on the number of risk factors present before the intervention. For each strategy, an investment appraisal assessed the extra costs and benefits of reducing a given PMWS severity score to the average score of a slightly affected farm. The net present value obtained for each strategy was then multiplied by the corresponding probability of success to obtain an expected value. A stochastic simulation was performed to account for uncertainty and variability. For moderately affected farms PCV2 vaccination alone was the most cost-efficient strategy, but for highly affected farms it was either PCV2 vaccination alone or in combination with biosecurity measures, with the marginal profitability between 'vac' and 'vac+bios' being small. Other strategies such as 'diets', 'vac+diets' and 'bios+diets' were frequently identified as the second or third best strategy. The mean expected values of the best strategy for a moderately and a highly affected farm were £14,739 and £57,648 after 5 years, respectively. This is the first study to compare economic efficiency of control strategies for PMWS and PCV2SI. The results demonstrate the economic value of PCV2 vaccination, and highlight that on highly affected farms biosecurity measures are required to achieve optimal profitability. The model developed has potential as a farm-level decision support tool for the control of this economically important syndrome.

Fig. 1

Batch production model framework of a farm operating with a 3-weekly-batch system.

Fig. 2

Relationship between expected losses and expected intervention costs for different strategies for farm scenario no. 4 (highly affected by PMWS and with all the risk factors present before intervention). In bold the best three strategies. The line symbolizes the loss-expenditure frontier.

Fig. 3

Net present value (NPV) obtained from the investment appraisal of implementing PCV2 vaccination as sole measure, and for different PMWS severities.

Fig. 4

Result of the model sensitivity analysis. The graph shows the mean expected value of the best strategy containing improvement of pig diets (‘diets’), reduction in stocking density (‘stock’) or improvement of biosecurity measures (‘bios’) as control measures for each scenario and with different level of intervention of these measures (diet: 4%, 5%, 6%, 7% and 8% increase in feed cost; stock: 9%, 10%, 11%, 12% and 13% reduction in stocking density; bios: −10%, 0%, 10%, 20% and 30% change in biosecurity cost from the baseline value). The graph also shows the expected value of PCV2 vaccination alone (‘vac’), as a control strategy, without any change in its costs. The expected values are obtained for an average PMWS highly affected farm. ‘MP present/free’ means presence or freedom of major pathogens on the farm; ‘high/low SD’ means that the farm has a high or low stocking density; ‘poor/good bio’ means that the biosecurity measures considered in this study are absent or present on the farm; and ‘poor/good diet’ means that the farm do not or do adjust well enough the diets given to the age groups of the pigs.