# Modelling Salmonella spread in a pig farm under three biosecurity strategies

Amandine Lurette, Catherine C. Belloc, Suzanne Touzeau, Thierry Hoch,

Henri H. Seegers, Christine Fourichon

► To cite this version:

Amandine Lurette, Catherine C. Belloc, Suzanne Touzeau, Thierry Hoch, Henri H. Seegers, et al. Modelling Salmonella spread in a pig farm under three biosecurity strategies. International Symposium of Salmonella and Salmonellosis (I3S), May 2006, Saint-Malo, France. 2006. *hal-02812895*

HAL Id: hal-02812895

https://hal.inrae.fr/hal-02812895

Submitted on 7 Aug 2023

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# Modelling *Salmonella* spread in a pig farm under three biosecurity strategies

A. Lurette<fnref n="1" />, C. Belloc<fnref n="1" />, S. Touzeau<fnref n="2" />, T. Hoch<fnref n="1" />, H. Seegers<fnref n="1" />, C. Fourichon<fnref n="1" />

<figure><img src="image_2.png" /></figure>

## INTRODUCTION

The production level is a critical point of the contamination of the whole pork supply chain by *Salmonella*.

**Objectives** : To estimate the number of shedder and carrier pigs at slaughter age under three biosecurity strategies.

## MATERIAL & METHODS

### 1. Development of a stochastic mathematical model to simulate:

* the pig population dynamics (Fig. 1) in a farrow-to-finish herd with batch farrowing management;

* the transmission of *Salmonella* depending on the contamination of the pen floor (Fig. 2).

<figure><img src="image_3.png" /><figcaption>Figure 1. Simplified farrow-to-finish herd production system. → flows linked to demographic processes → flows controlled by producers</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Figure 2. Epidemiological model.</figcaption></figure>

**Contact structure** influenced by:

* the variability in reproduction and in growth,

* the producers' management, → leading to variations in the transmission.

**Groups of slaughtered pigs** were issued from several batches depending on their weight.

**Parameters** : from published literature and expert opinion.

### 2. The three biosecurity strategies differ only for finishing pigs:

**AIAO** strict all-in/all-out management with complete cleaning, disinfection and drying period between batches;

**NDP** all-in/all-out allowing the suppression of the drying period;

**BM** management allowing the suppression of the drying period and batch mixing.

### 3. Simulations were run after the introduction of a shedder gilt in a AIAO herd. After equilibrium, the 3 strategies were implemented.

## RESULTS

The number of batches in a group of slaughtered pigs was significantly higher under the BM strategy (Tab. 1).

<table><caption>Table 1. Proportion of groups of pigs at slaughter per number of batches under the three biosecurity strategies.</caption><thead><tr><th rowspan="2">Biosecurity strategy</th><th colspan="4">Number of batches</th></tr><tr><th>1</th><th>2</th><th>3</th><th>&gt;3</th></tr></thead><tbody><tr><td>AI/AO</td><td>0.18</td><td>0.34</td><td>0.30</td><td>0.18</td></tr><tr><td>NDP</td><td>0.21</td><td>0.35</td><td>0.27</td><td>0.17</td></tr><tr><td>BM</td><td>0.15</td><td>0.20</td><td>0.31</td><td>0.34</td></tr></tbody></table>

Prevalence of shedder and carrier pigs varied widely between batches, within and between strategies (Fig. 3).

<figure><img src="image_5.png" /><figcaption>Figure 3. Prevalence of shedders & carriers at slaughter age.</figcaption></figure>

Mean prevalence differed significantly between strategies. **AIAO**: 0.27±0.04, **NDP**: 0.45±0.02, **BM**: 0.53±0.01.

## DISCUSSION & CONCLUSION

A less strict management increased dramatically the number of shedder and carrier pigs at slaughter age.

Further validation of the model based on field data is considered.

Both the heterogeneity of the contact structure and the biosecurity strategies play a major role in pathogen transmission in a farrow-to-finish herd.

<footnote n="1">¹Unit of Animal Health Management, Veterinary School - INRA, BP 40706, 44307 Nantes Cedex 3, France.</footnote>

<footnote n="2">²Unit of Applied Mathematics and Computer Science, INRA, 78352 Jouy-en-Josas Cedex, France.</footnote>