Sampling effort

5.4.1.1 Fox data

Webbon et al. (2004) estimated the total rural fox population in GB to be 225,000 foxes (95% confidence interval 179,000-271,000). The population was estimated to be highest in central and southern Scotland and southwest England. Urban foxes were not included in the population density map.

A total of 2945 wild foxes were sampled forTrichinellabetween 1999 and 2006. Ten

foxes did not have location, date or age information recorded. These were excluded from further analysis. The highest densities of sampled foxes were in the north, southeast and southwest of England.

The sampling effort for foxes included foxes tested between 1999 and 2006 (see Figure

5.2in Appendix 1). The highest level of sampling in relation to estimated fox population

density was in the Scottish Borders.

5.4.1.2 Horse data

The horse population data included 873,596 horses. There were 10.7% for which the age was unknown. Of horses whose age was known, the average age was 11.8 years, with a median of 10.0 years and a mode of 8.0 years. There was a long tail to the right of the distribution, with the oldest horses aged 39 years (n = 1383).

The NED data was supplied as the number of horses by county, with location infor- mation being unavailable for 13.8% of horses. The highest count of horses was in Devon (n = 45,206; 5.2% of all horses) followed by Lancashire (3.5%). Across all ages, horses were widely distributed across England. There were low-density areas in the east and north and across Scotland. Wales had a relatively high density of horses in the south (following the pattern of human population density) but few elsewhere.

We received data from six abattoirs but expect there are others where horses are slaughtered. The distribution of horses slaughtered across GB was weighted by the population density, abattoir size and abattoir location. This led to the highest densities

Table 5.3: Estimated number of pigs present by sub-population in England, Scotland and Wales

Low-risk High-risk Low-risk High-risk

Country breeder breeder grower grower Total pigs England 381,617 142,015 2,846,923 934,917 4,305,472

Scotland 55,569 0 383,280 0 438,849

Wales 4,604 0 26,053 0 30,657

Great Britain 441,790 142,015 3,256,256 934,917 4,774,978 9.25% 2.97% 68.19% 19.58% 100.00%

of slaughtered horses around the West Midlands, Tyne and Wear and the south of Wales. A total of 45,005 horses were slaughtered.

Sampling effort for horses included horses slaughtered across all years of data pro-

vided (see Figure5.3 in Appendix 1). It was assumed that all slaughtered horses were

tested forTrichinella. The highest sampling densities were seen in Scotland and Wales.

5.4.1.3 Pig data

The pig population in Great Britain was estimated at 4,774,978 pigs (Table5.3). The

population was most densely concentrated in the Norfolk/Suffolk, Humberside/Yorkshire and Grampian regions. The Defra records of properties classified as piggeries included 21,887 English holdings, 1153 Scottish holdings and 2509 Welsh holdings (total number of properties 25,549). Approximately 10,000 commercial piggeries exist, with around 2000 providing 92% of total pig meat production (A. Knowles, pers. comm.). Census 2005 data included records for 794 holdings where pigs were kept outdoors.

The pattern of both grower and breeder pigs being reared in low-risk accommodation was similar to that of the whole pig population. Grower and breeder pigs living in high- risk accommodation are found mainly in the east of England and Cumbria.

Abattoir throughput increased each year, with 7,654,466 pigs slaughtered in 2002 by the 192 abattoirs that responded to the FSA survey (FSA 2003). The estimated num-

bers of pigs slaughtered by sub-population and country for 2005 are given in Table5.4.

Slaughtered low-risk breeders were mainly from the east coast, from Suffolk, Norfolk, Humberside, Yorkshire and Grampian regions. High-risk breeder pigs were mainly from Suffolk, with smaller clusters in Cumbria and a few other counties. Low-risk grower pigs were slaughtered from locations in a similar pattern to low-risk breeders, although there were higher densities of grower pigs slaughtered in the western and southern ar- eas. There were fewer high-risk grower pigs slaughtered, and these were mainly located in the east of England. The density pattern for all pigs slaughtered was similar to that for low-risk grower pigs, which was expected due to the large proportion of this group of pigs in the population.

Table 5.4: Estimated number of pigs slaughtered per year by sub-population and coun- try

Low-risk High-risk Low-risk High-risk

Country breeder breeder grower grower Total pigs England 148,638 55,382 7,967,696 2,837,824 11,009,540

Scotland 21,681 0 1,092,330 0 1,114,011

Wales 1,757 0 82,189 0 83,946

Great Britain 172,076 55,382 9,142,215 2,837,824 12,207,497

Table 5.5: Estimated number of pigs tested in 2005 by sub-population and country Low-risk High-risk Low-risk High-risk

Country breeder breeder grower grower Total pigs England 126,437 39,927 916,291 289,355 1,372,010

Scotland 6,759 0 48,979 0 55,738

Wales 173 0 1,256 0 1,429

Great Britain 133,369 39,927 966,526 289,355 1,429,177

There were a total of 43 records from 13 abattoirs that tested pigs for Trichinella

between 1993 and 2002. Not all abattoirs indicated that they tested pigs in all years. There was a peak of testing in 1998 with 2,914,651 pigs sampled, whereas in 2002 1,228,520 pigs were tested. Fourteen percent of slaughtered grower pigs and 86% of slaughtered breeders were estimated to be tested. Seventy-six percent were estimated to be kept indoors with the remainder either outdoors or in combination systems. Table

5.5gives the estimated number of tested pigs by country and sub-population in 2005.

Pig sampling effort was calculated for each of the four sub-populations (high- and low-risk breeder and grower pigs) using the estimated number of pigs slaughtered in one year. Low-risk grower pigs were uniformly sampled across the country, with the

exception of west and northern Scotland (see Figure 5.4 in Appendix 1). High-risk

grower pigs were slaughtered in a uniform pattern across England in relation to the

underlying population (see Figure5.5in Appendix 1). Relative to their sub-population

low-risk breeders were most highly sampled in the north-west of Scotland (see Figure

5.6in Appendix 1). Sampling effort for high-risk breeders (see Figure5.7in Appendix

1) followed a similar pattern to the high-risk grower population.

5.4.2 Upper confidence limit (95%) for the estimate of prevalence