Investigation of Land Coverage and Elevation as Risk Factors for PRRS Breaks - Dr. Andreia Arruda, from the 2016 Allen D. Leman Swine Conference, September 17-20, 2016, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2016-leman-swine-conference-material

1. Investigation of land coverage
and elevation as risk factors for
PRRS breaks
Andreia Arruda, DVM PhD
University of Minnesota

2. Background
Cumulative PRRS incidence 2009-2017 (SHMP)

3. Background

4. Background

5. Background

6. Background

7. Objective
Investigate whether land elevation and
coverage are associated with PRRS breaks
- Account for important factors of interest
- Use data from swine sites spread across the
country

8. Methods
Data source: SHMP (n=706 sow herds), 2009-
2016
Variables of interest:
• Terrain elevation
• Land coverage
• Swine density
• Geographical region
• Herd size

9. Methods
Density of swine sites participating in the SHMP

10. Methods
Density of swine sites (FAO, modelled; 2005)

11. Elevation
• The height of a terrain
– Absolute number – altitude (meters above sea level)
– Relative number – slope, steepness as compared to
other features in the area
run
rise
Slope =
rise
run
e.g.
20 𝑓𝑓𝑓𝑓
100 𝑓𝑓𝑓𝑓
= 0.2 or 20%
86m
80m
86m
1m = 3.3 ft

12. 1
2
3
4
5
Slope
Published 2007-02-16
NASA Shuttle Radar Topographic Mission (SRTM), 2006
USGS Geological Survey (GTOPO30), 2002
1- 2% (8%)
2-5% (35%)
5-8% (43%)
8-16% (10%)
16-30% (5%)
30-45% (0)
> 45% (0)

13. Altitude
The CGIAR Consortium for Spatial Information
NASA Shuttle Radar Topographic Mission (SRTM), 2006
USGS Geological Survey (GTOPO30), 2002
1: <185m (25%)
2: 185 - 316m (25%)
3: 317 - 391m (25%)
4: > 391m (25%)

14. Land Coverage
Joint Research Centre (European Commission)
Global Land Cover 2000 Project (GLC2000)
1: cultivated and managed areas (67%)
2: shrubs/ herbaceous cover (e.g. pasture) & others (14%)
3: tree cover, needle-leaved or mixed (9%)
4: tree cover, deciduous broad-leaved (11%)

15. Methods
Outcome of interest: number of breaks
Statistical model: Multilevel mixed-effects
Poisson regression
• Backwards stepwise approach
• Random effect for production system
• Statistical significance declared at P < 0.05

16. Results
• Mean 1.4 outbreaks per year per site
• 40% farms never reported a break

17. Variable¶ IRR P-value
Density 1.46 <0.001*
N animals 1.30 0.001*
Land coverage Shrubs, herbaceous 0.70 0.04*
Needle-leaved trees 0.56 0.003*
Broad-leaved trees 0.42 0.009*
Slope 2-4% 1.01 0.95
5-8% 0.77 0.10
9-16% 0.44 0.001*
17-30% 0.18 0.006*
Region MN/IA 1.59 0.001*
NC 0.83 0.60
NE 0.70 0.06
Other 0.49 0.001*
OK 1.28 0.38
PA 0.58 0.36
Results
¶Refs- low density, low N animals, land coverage as cultivated/
managed areas, slope 1% or <, region IL
Results should be
interpreted with
caution due to the
cross-sectional
nature of the data

18. • Large number farms across many US regions
• Land inclination
– Airborne transmission
– Proxy for other factors
• Vegetative filters
Discussion

19. Take-home messages
- We investigated whether land elevation
and coverage are associated with PRRS
breaks.
- “Highly inclined terrains” were associated with
fewer breaks
- Presence of shrubs and trees were associated with
fewer breaks compared to cultivated areas

21. Acknowledgements
University of Minnesota, College of Veterinary
Medicine
B. Morrison, C. Vilalta, A. Perez
SHIC
SHMP
Swine veterinarians and producers that share
data

22. Thank you!
arrud002@umn.edu