Cost of post-weaning multi-systemic wasting syndrome and porcine circovirus type-2 subclinical infection in England - an economic disease model

Abstract

Post-weaning multi-systemic wasting syndrome (PMWS) is a multi-factorial disease with major economic implications for the pig industry worldwide. The present study aimed to assess the economic impact of PMWS and porcine circovirus type 2 (PCV2) subclinical infections (PCV2SI) for farrow-to-finish farms and to estimate the resulting cost to the English pig industry. A disease model was built to simulate the varying proportions of pigs in a batch that get infected with PCV2 and develop either PMWS, subclinical disease (reduce growth without evident clinical signs) or remain healthy (normal growth and no clinical signs), depending on the farm level PMWS severity. This PMWS severity measure accounted for the level of post-weaning mortality, PMWS morbidity and proportion of PCV2 infected pigs observed on farms. The model generated six outcomes: infected pigs with PMWS that die (PMWS-D); infected pigs with PMWS that recover (PMWS-R); subclinical pigs that die (Sub-D); subclinical pigs that reach slaughter age (Sub-S); healthy pigs sold (H-S); and pigs, infected or non-infected by PCV2, that die due to non-PCV2 related causes (nonPCV2-D). Enterprise and partial budget analyses were used to assess the deficit/profits and the extra costs/extra benefits of a change in disease status, respectively. Results from the economic analysis at pig level were combined with the disease model's estimates of the proportion of different pigs produced at different severity scores to assess the cost of PMWS and subclinical disease at farm level, and these were then extrapolated to estimate costs at national level. The net profit for a H-S pig was £19.2. The mean loss for a PMWS-D pig was £84.1 (90% CI: 79.6-89.1), £24.5 (90% CI: 15.1-35.4) for a PMWS-R pig, £82.3 (90% CI: 78.1-87.5) for a Sub-D pig, and £8.1 (90% CI: 2.18-15.1) for a Sub-S pig. At farm level, the greatest proportion of negative economic impact was attributed to PCV2 subclinical pigs. The economic impact for the English pig industry for the year 2008, prior to the introduction of PCV2 vaccines, was estimated at £52.6 million per year (90% CI: 34.7-72.0), and approximately £88 million per year during the epidemic period. This was the first study to use empirical data to model the cost of PMWS/PCV2SI at different farm severity levels. Results from this model will be used to assess the efficiency of different control measures and to provide a decision support tool to farmers and policy makers.

Fig. 1

Structure of epidemiological within-farm PMWS disease model.

Fig. 2

Percentages of each type of pig in a batch at different PMWS severity levels. Where: H-S are healthy pigs with normal growth; PMWS-D are PMWS pigs that die due to the disease; PMWS-R are PMWS pigs that recover from the disease; Sub-D are PCV2 infected pigs with slow growth, no clear PMWS clinical sign and that die; Sub-S are PCV2 infected pigs with slow growth, no clear PMWS clinical sign and that survive; and nonPCV2-D are pigs that die due to non PCV2 related causes.

Fig. 3

Cost of PMWS and PCV2 subclinical infection (PCV2SI) at farm level and at different PMWS severity levels using 2010 data (deterministic model output). Where: PMWS-D are PMWS pigs that die due to the disease; PMWS-R are PMWS pigs that recover from the disease; Sub-D are PCV2 infected pigs with slow growth, no clear PMWS clinical sign and that die; and Sub-S are PCV2 infected pigs with slow growth, no clear clinical sign and that survive.

Fig. 4

Cost of PMWS and PCV2 subclinical infection (PCV2SI) at farm level and at different PMWS severity levels using 2010 data (stochastic model output). Straight lines shows the mean values and the dotted lines correspond to the 90% confidence intervals.

Fig. 5

Total combined PMWS and PCV2SI cost for the whole English pig industry from 2001 to 2008. (*) Based on pseudo-PMWS severity estimations. Benchmarking data for the years 2001 to 2008 was used for the following parameters: (1) litters per sow per year, (2) piglets born alive per litter, (3) pre-weaning mortality, (4) sow feed price per tonne, (5) grower feed price per tonne, (6) Vet & Med cost per pig, (6) Electricity cost per pig, (7) Water cost per pig, (8) Straw & Bedding cost per pig, (9) transport cost per pig, (10) miscellaneous or LII cost per pig, (11) labour cost per pig, (12) building cost per pig, (13) equipment cost per pig, (14) other fixed cost per pig, (15) deadweight average price per kg and (16) number of breeding sows.

Fig. 6

Costs of PMWS, cost of PCV2SI and profitability of the farm at different pig deadweight kilogram prices (DAPP) values. The corresponding ‘DAPP’ is written above its ‘total profit’ line.