Impact and control of pathogens on poultry
Pathogens can be introduced to a poultry flock via air, pests, people, water and feed. Their prevalence and impact is largely dependent upon the quality of the environment and the health and welfare of the birds. Healthy birds have a higher tolerance to performance-limiting pathogens than stressed animals.
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.
“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.”
“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,...
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