Impact and control of pathogens on poultry

Pathogens, disease-causing microorganisms including fungi, bacteria and protozoa, are associated with increased veterinary costs, poor flock uniformity, increasing concomitant diseases, reduction in enterprise profitability and ultimately with risks to animal welfare and human health. This article, will look at where and how pathogens can be introduced to a poultry operation, why feed is so commonly overlooked as a vector and how good husbandry practices and biosecurity can reduce their presence and avoid non-compliance.

Vectors for pathogen transfer can be mechanical and biological. Traditional biosecurity programmes have prioritised vectors such as people, vehicles, rodents and insects, limiting unnecessary visits from personnel and requiring high risk visitors, including veterinarians and other professionals who have reason to visit other poultry production facilities, to change clothing and footwear and sterilise/disinfect equipment before entering the site. Today’s most comprehensive biosecurity programmes also cover water and, increasingly feed, in a bid to control the presence and impact of performance limiting pathogens, as poultry pathogen control specialist Dr Gino Lorenzoni explains: “Feed and water quality have long been identified as a key influencing factor on the gastro-intestinal health of farmed animals. Anti-nutritional factors of grains, mainly moulds and mycotoxins, have received lots of attention from nutritionists and veterinarians around the globe, in part due to extensive technical and marketing campaigns by solutions providers.”

Dr Gino Lorenzoni is a poultry veterinarian with a PhD in avian physiology and immunology from University of Arkansas and several years of experience in the poultry industry as a technical advisor. He moved to Europe in 2015, taking on the role of technical director at global pathogen control specialist Anitox.

Recontamination risk

“Trials designed to monitor the risk of changes in bacterial load once feed leaves the mill show that recontamination can occur all the way to the feed tray. Storage of finished feeds, for example, is part of the problem. Pellets are stored in silos where temperatures vary between day and night, leading to condensation on silo walls. This humidity reaches the feed, creating a much more appealing media for bacterial growth. In addition to this, dust inside the silos tends to adhere to the walls. If a silo is not cleaned regularly, a crust of dust and decaying material starts developing inside the silo walls. With the vibrations generated during the loading of the feeders, decaying material in the form of crusts detaches and mixes with the feed. This results in the millions of bacteria and mould contained in these crusts serving as nuclei for contamination of the fresh feed that now surrounds them.

“Research shows that by the time feed reaches feeders, we can expect to see an increase in contamination levels of somewhere between 4 and 20 times levels measured at the feed mill. At that point we can predict that more than 10% of the pelleted feed consumed by animals would exceed 10,000 times the maximum permissible bacterial contamination levels suggested for drinking water.

“And the situation is even more challenging in systems that feature mash feed, as is the case in most layer operations, for example. Mash production doesn’t require the application of heat and therefore does not involve even the most basic bacterial control phase in its production. That means that the full extent of bacterial contamination contained in raw materials goes into the finished feed and straight to the animals.

“Our sample analysis shows that in Europe from 2010 to 2015 the average contamination from enterobacteriaceae in mash feed is 80,000 cfu/g of feed at the feed mill level, with the top 10% most contaminated samples averaging over 700,000 cfu/g of feed. If we consider a modest 5-fold increase in bacterial contamination during storage, we can predict that at the feeder levels may average 3,500,000 cfu/g, 35,000 times greater than the maximum contamination level recommended for drinking water.”

An animal’s ability to withstand other diseases will be adversely impacted if they are continuously challenged. Photo: Jan Willem van Vliet

Safe limit

“It is difficult for facility managers and biosecurity programme authors to establish a ‘safe’ limit for enterobacteriaceae in feed. Few organisations are willing to venture a number, and those that do – Europe’s Product Board for Animal Feed, for example – do so based on specific challenges. It suggests 100 bacteria/g mark as a desirable level, most likely because of increased risk of Salmonella contamination as enterobacteriaceae counts rise.

“When standards are set for drinking water to be consumed by food producing animals a different approach is usually taken. A level of 50 coliforms per ml has been recommended by several institutions including North Carolina State University and Mississippi State University. Why, then, is water more commonly scrutinised for bacterial contamination than feed?

“One possible answer is that animal feed can be pelleted – a process which involves the application of heat that, in turn, can offer some control of initial bacterial loads. But having looked carefully at analysis of 10,000 European feed mill samples taken by Anitox between 2010 to 2015, we found that enterobacteriaceae levels in pelleted feed averaged 3,700 cfu/g, 74 times greater than the limit suggested for contamination in water.“ “Even considering that animals drink twice as much as they eat, that would still see consumption of feed-source enterobacteriaceae at 37 times the level deemed acceptable according to water standards.”

As feed is normally the number one cost related to poultry production, it’s unsurprising that all comprehensive biosecurity programmes now address the issue of feed quality, and specifically pathogen load in respect to Salmonella risk, in detail. It has been calculated that feed comprises around 80% of the overall cost of broiler production. Thus, the ability of animals to effectively digest and absorb the nutrients contained in feed will dictate how profitable an operation will be.

“The more competitive the markets get in terms of profit per kg of produced protein, the more important it becomes to be able to extract the most out of feed to maintain a healthy business,” explains Dr Lorenzoni. “A healthy intestine is designed to maximise its absorptive and digestive surfaces. Intestinal mucosa is composed of millions of slender villi that, when combined, massively amplify the available surface. When enteritis arises – commonly as a result of pathogen load spikes in feed coinciding with times of stress such as dietary or regime change – the cells that compose the villi cannot survive long enough to create the tall and slender structure. The result is that blunt and short villi are formed. As a consequence, part of the absorptive surface is lost, reducing the overall capacity of the intestine to absorb nutrients.”

Dr Gino Lorenzoni, global pathogen control specialist at Anitox: “Research shows that by the time feed reaches feeders, we can expect to see an increase in contamination levels of somewhere between 4 and 20 times levels measured at the feed mill.” Photo: Anitox

Feed risk underestimated

So, why has microbial contamination of water traditionally been a focus, while feed, for example, has not? “It is possible that producers tolerate feed microbial variation precisely because it varies from batch to batch rather than presenting a constant level of challenge, as with water,” explains Dr Lorenzoni. “The same source of water is likely to give a similar microbiological profile for a significant amount of time, while feed quality can change as soon as we receive a fresh batch of feed, which could mean only a couple of days in some cases. Frequently at farm level we see animals with mild enteritis. When the enteritis starts, the farm manager looks for solutions, calls the veterinarian and the nutritionist and before any of the plausible solutions have had time to be implemented, the enteritis is gone. Things return to normal without the need for formal treatment. But those bouts of enteritis are having an effect on productivity.”

“In truth, there are many factors that will determine the effect of consuming contaminated feed. The species of bacteria present will have a tremendous impact. While some organisms present in feed may cause only a modest impact on the nutrients available in the diet, others cause direct damage to the animals. Pathogenic E. Coli will produce enteritis even if the feed is relatively free of other bacteria. In most cases, however, it is difficult to predict the outcome of bacterial load; there are simply too many complex factors at play. Debilitating factors, immune competency of the animals (including the presence of immune suppressive agents), current and recent diseases, and the physiological stage of the animals, all have a profound impact on the outcome of consuming contaminated feed.

Long term approach – to address the problem source

“Bacterial load in feed can cause severe intestinal disease in animals, but that won’t always be the case. Most of the time the outcome of a single event – a peak in bacterial load leading to enteritis, for example – is not spectacular and usually affects only one part of the farm for perhaps a day or 2. For this reason the importance of these events can be overlooked; they are simply not big enough to top a producer’s list of concerns. But overlooking them could significantly impact on productivity. An animal’s ability to withstand other diseases will be adversely impacted if they are continuously challenged. If another disease develops, then the solution sought will focus on targeting the new disease, not on targeting the debilitating factors that increased the risk of susceptibility. This approach may offer a short term solution and the disease threat solved, but a different disease will follow shortly and the underlying problem is thus not addressed.”

Transmission route

Feed is undoubtedly a transmission route for bacterial pathogens including Salmonella, E.coli, Listeria, Clostridium, Staphylococcus and more (Uwaezuoke et al, 2008). It is also possible that viruses including the Avian Influenza (bird flu) virus can survive in and be transferred to farmed birds through unprotected feed. Feed materials, such as wheat, can act like ‘sponges’ and pick up pathogens from the point of pick, through the feed mill and right up to delivery onto a farm. High, and varying levels, of pathogen load in feed ingredients vary based on ingredient type, season and supplier. Wet harvests, for example, are associated with mouldy grains which can lead to high mycotoxin content. Some types of feed materials pose more of a risk than others; for example animal-by products such as fish meal and rendering meal, DDGS and soya can be heavily contaminated with bacteria.

The routine use of antibiotics as growth promoters was banned in Europe in 2006, and the spotlight has now firmly focused on controlling pathogens much earlier in the production cycle, to reduce the incidence of diseases such as necrotic enteritis, caused by Clostridium, thus reducing the need for remedial antibiotic treatments.

True heat treatment (over 86°C for 6 min) although damaging nutrients can ensure feed is free from pathogens. However, as it offers no residual protection, recontamination risk remains a significant challenge. Organic acid treatments composed of individual acids and blends of several acids have been found to perform antimicrobial activities (Wang et al, 2009), however, their residual protection varies significantly and diet density is affected as significant quantities need to be added to have any impact on pathogens.

The latest feed protection technology offers better protection

The latest generation feed protection technology, based on synergistic blends of carboxylic acids and phytochemicals, has proven to offer much greater protection against feed-source pathogens. The UK Government’s Animal and Plant Health Agency (APHA) compared Anitox’s next generation Finio product with 3 leading traditional organic acid blends to test for control of Salmonella in feed. The trial demonstrated that the latest technology was significantly more effective at all concentrations at reducing Salmonella. It also demonstrated that the new technology offered residual protection in feed for up to 14 days.

References are available upon request.