Beef safety and environmental protection are important aspects of feedlot production. Reporters have blamed intensive livestock operations or “factory farms” as the primary sector responsible for contaminating food and water sources with pathogenic bacteria that make humans ill. Extremists have called for drastic regulations to curtail or ban intensive livestock production. Environmental or food safety fears have been raised in communities when feedlot producers have wanted to expand or build a new operation.
Given a lack of scientifidata to allay these fears or put risks into perspective, it has been difficult for the feedlot industry and governments to manage these issues. Some government officials have called for the use of the “precautionary principle” in writing regulations for livestock production. It states when you don’t know the risk of something, you assume the worst and move towards zero risk.
We have seen the precautionary principle used in Europe to remove antimicrobials from livestock feeds and ban the use of hormones. We have seen these fears in Canada result in a ban on the development of new intensive livestock operations. Policy based on the precautionary principle can have devastating consequences on the viability of livestock production. The only way feedlot producers can deal with the precautionary principle is to support research that generates scientifically valid and accurate risk assessments.
One such study funded by the Alberta beef industry and government gathered representative baseline data on the occurrence of zoonotic bacteria in Alberta feedlots. Zoonotic bacteria are found in animals and cause disease in humans. The study was a joint effort involving myself and researchers at the Vaccine and Infectious Disease Organization (VIDO), Alberta Agriculture, Washington State University, and USDA.
Samples were taken spring and fall from 21 randomly selected feedlots with at least a 5,000-head capacity throughout Alberta. We sampled manure in the pens of cattle at the start and near the end of the feeding period, and we sampled carcasses from the same feedlot pens in the cooler as well as water from the catch basins and shallow and deep soil samples before and after manure applications. All these samples were tested for generic E. coli, a normal bacterium found in the fecal matter of animals and humans, and three potentially zoonotic bacteria: E. coli O157, salmonella, and campylobacter.
As expected, generic E. coli were found in almost every manure sample from the feedlot pens. If this bacterium is found, it simply indicates the presence of feces. Escherichia coli O157 were found much less frequently, in 10 per cent of the spring manure samples and four per cent of the fall manure samples. These bacteria were more common in the shortest-on-feed pens (four per cent) than the preslaughter pens (one per cent). About half of the pens had at least one positive isolate of E. coli O157.
Salmonella were rare, only one per cent of the samples were positive. Within that small number various serotypes were identified, including S. Rublislaw, S. Saintpaul, S. Mbandaka, S. Enteritidis, S. Typhimurium, and S. 4,5,12:8.
Campylobacter were found in 76 per cent of the manure samples; 66 per cent of the isolates were C. jejuni and one per cent were C. coli. Both can cause disease in humans. The bacteria occurred with the same frequency in spring and fall; however, it was more commonly isolated in preslaughter pens of cattle (88 per cent) than in shortest-on-feed pens (64 per cent).
This study supports the findings of other research indicating manure is a potential source of E. coli O157, salmonella, and campylobacter serotypes that may be pathogenic to humans if exposed through consumption of fecal contaminated food or environmental sources.
Sampling at the plant, however, suggests federal processing plants have implemented effective HACCP systems and the risk of bacterial contamination from beef carcasses is very low after they’ve been steamed and cleaned. Only one positive sample of generic E. coli and one positive sample of
C. jejuni were found on the carcasses of these feedlot cattle during the spring and both were sensitive to all antimicrobials tested. None of the carcasses tested positive for salmonella. We were not allowed to test for E. coli 0157 in the federal plants; however, given the low level of generic E. coli on carcasses, it is likely that the occurrence of E. coli O157 on beef carcasses was equally rare.
Catch basins that collect runoff from these feedlot pens
had similar levels of generic E. coli in the spring (62 per cent) and fall (52 per cent). However, E. coli O157 (29 per cent), salmonella (five per cent), and campylobacter (52 per cent) were only found in spring water samples, suggesting environmental factors may affect bacterial survival and/or growth. None of the campylobacter serotypes isolated in catch basis water were pathogenic to humans. Catch basin water either evaporates or is irrigated onto feedlot silage crops and we don’t know if this increases the risk of infection in cattle that consume the silage.
Generic E. coli were isolated from soils samples before and after manure applications. E. coli O157 and salmonellae were occasionally isolated from soil samples (three per cent) but they weren’t related to the timing of the manure application. Campylobacter were found in 35 per cent of the spring soil samples but only three per cent of the fall samples. Only one of the positive isolates was C. jejuni.
To summarize, our results found that while generic E. coli and campylobacter spp. were commonly found in the manure of Alberta feedlots, E. coli O157, salmonella, C. jejuni, and C. coli were much less frequently isolated from beef carcasses, feedlot catch basin water or the soil used to grow feedlot silage before and after manure applications. A quantitative risk assessment would be needed to determine the level of risk to human safety from these sources.
Scientific manuscript available at Canadian Veterinary Journal, 2009: 50: 166-172.
— Dr. Joyce Van Donkersgoed