Livestock and wildlife proximity

• Both livestock and wildlife can be sources of contamination for fresh produce via direct contact or environmental vectors.
• Key transmission routes include runoff and contaminated irrigation water, less critical transmission routes include windborne dust and insects (e.g. filth flies).
• Livestock should be separated from produce fields by appropriate buffer zones, fencing, and physical barriers.
• Wildlife exclusion is more difficult but important; a site-specific risk-based approach is advised.
• Certain species, particularly deer and wild boar, present higher risk due to their mobility and potential pathogen carriage.
• The highest risk of contamination is when the edible portion of the crop contacts faecal material, directly or indirectly.

The presence of livestock or wildlife near fresh produce cultivation areas poses a recognised risk of contamination with zoonotic pathogens such as Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Cryptosporidium spp. These organisms may be carried asymptomatically by animals and shed in their faeces, contaminating soil, water, or the crops directly. Though the frequency of contamination is generally low, the potential consequences for public health and market confidence are severe, especially as many implicated crops are consumed raw.

Contamination from livestock can occur through a variety of environmental routes, particularly when animals are kept near growing land. Rainfall can mobilise faecal material and pathogens from nearby fields or pastures, allowing them to be transported by overland flow or runoff. The risk is greatest where land slopes towards growing areas or drainage channels are shared. A Scottish study found E. coli O157:H7 in soil and leaf samples up to 180m from grazing cattle during wet weather, indicating the potential for indirect contamination through surface water and splash dispersal (1).

In the UK, an estimated 70 million tonnes of manure are produced annually from intensively farmed livestock, with a similar amount from extensively reared animals (2). Although not all this manure contains zoonotic pathogens, 10–30% of fresh samples do contain microorganisms capable of infecting humans (see Table 1 below). Research commissioned by the Food Standards Agency in the early 2000s surveyed farms across England, Scotland, and Wales to estimate the prevalence of such pathogens. The results, reporting the percentage of positive samples and the levels of contamination for five key foodborne illness pathogens are summarised in Table 13.

Table 1: The percentages of GB domestic livestock wastes that tested positive for each of the zoonotic agents listed. ND = not determined.

Flies, particularly filth flies such as the house fly (Musca domestica) and blow flies (Calliphora vomitoria), can also act as mechanical vectors, transferring pathogens from livestock faeces or slurry to nearby produce fields (4-7). In the UK, stable flies (Stomoxys calcitrans) and blowflies are commonly associated with farms and waste management sites. Studies have shown these insects can carry viable E. coli O157:H7 and Salmonella spp. for several hours, posing a contamination risk when farms and cropping areas are in close proximity (4-7). 

While large livestock operations are more readily managed, the risks posed by wildlife are more difficult to control. Birds, rodents, deer, and other wild animals are known carriers of zoonotic pathogens and can contaminate crops through faecal droppings, especially if they feed or roost in fields (8). For instance, wild deer populations in Scotland have tested positive for E. coli O157 and Cryptosporidium spp., though the prevalence is generally lower than in livestock (9-11). Even low prevalence may be significant due to the low infectious dose of E. coli O157:H7. Faecal contamination from birds (especially gulls, pigeons, and corvids) is also a concern, particularly near open reservoirs or fields where birds congregate in large numbers (8).

The role of rodents, such as rats and field mice, should not be underestimated. These animals can deposit faeces directly onto crops or contaminate stored produce. Studies from UK farm environments have found Salmonella spp. in wild rodents at low but detectable levels (8, 12).

Compared to livestock, much less is known about the prevalence and levels of zoonotic pathogens in wildlife manure. However, a detailed review by Simpson provides valuable insights (8). Below is a non-complete summary (Table 2) of British wildlife species known to harbour zoonotic pathogens. This table is not exhaustive but does highlight some less obvious species that growers may not typically associate with contamination risks. 

There have been documented cases where the same zoonotic pathogen was found in crops, irrigation water, and wildlife - although the direction of transmission (i.e. whether the wildlife contaminated the crop or vice versa) is often unclear. Table 2 aims to alert producers to possible wildlife vectors that may not have been fully considered.

Table 2: A selection of the zoonotic pathogens that can colonise animals in the UK

Wild and domestic animals may use the same landscape corridors, including hedgerows, streams, and ditches, which can act as routes for cross-contamination. Shared access to irrigation water can further elevate risks. While physical exclusion (e.g. fencing or netting) is often more feasible for livestock, it may be cost-prohibitive or impractical for managing wildlife. Risk mitigation strategies should therefore be proportionate and based on local wildlife pressure, cropping system, and intended crop use (raw vs processed).

The United States Department of Agriculture (USDA) recommends a minimum 120-metre buffer zone between leafy green fields and livestock to reduce, though not eliminate, the risk of pathogen transmission (24). While this specific guidance originates in the US, similar principles are reflected in UK agricultural practices, particularly within assurance schemes such as Red Tractor and LEAF Marque. For instance, Red Tractor’s Fresh Produce Standards require growers to perform documented, risk-based assessments of water sources, adjacent land use, and wildlife pressures, alongside implementation of appropriate mitigation strategies (25). LEAF Marque also mandates site management to reduce contamination risks from neighbouring land and wildlife activity (26). Currently, neither the Food Standards Agency (FSA) nor Food Standards Scotland (FSS) impose statutory minimum buffer distances. Instead, the UK’s approach emphasises a systems-based food safety strategy (see list of potential interventions below). Buffer zones are viewed as one control among several interlinked measures including microbiological testing and treatment of irrigation water, management of animal access and wildlife exclusion, and good hygiene practices during irrigation and harvest (27).

For a systems-based approach preventive measures can include:

• avoiding cropping on land directly adjacent to livestock housing or manure storage
• creating buffer zones and vegetative barriers between grazing land and produce fields
• monitoring for wildlife activity and applying deterrents where needed
• managing habitat features (e.g. long grass, open water) that may attract animal activity
• assessing the placement of water sources, especially untreated surface water used for irrigation
• install/ensure appropriate treatment of irrigation water
• good hygiene practices during irrigation and harvest

In conclusion the primary concern for UK and Scottish growers are water-borne transmission via contaminated irrigation water and surface run-off. Buffer zones and other mitigation measures are most effective when incorporated into a wider, systems-based food safety framework tailored to local conditions.