Zootecnica International - World Poultry Journal

Mr. Jeffrey P. Griggs
Research Assistant
University of Minnesota
Dept. of Animal Science
St. Paul, MN, U.S.A

Food-borne illness can be caused by a large number of different infectious agents. The pathogens that cause food-borne illness can be viruses, bacteria, or parasites. According to Mead et al. (1999) the two most common bacterial causes of food-borne illness are Campylobacter spp. and Salmonella spp. They estimate that these two genera of bacteria cause about 24% of all food-borne illnesses in the United States. This equates to over 3.3 million cases of food-borne illness per year from Campylobacter and Salmonella alone. The human illnesses caused by these bacteria are similar. The symptoms of each last about 1 week and are fever, abdominal cramps and diarrhea. Both of these organisms can be contracted from the consumption of poultry, and both can be prevented by thoroughly cooking poultry to an internal temperature of 165oF before consumption.

Most chickens carry Campylobacter in their intestinal tract. These bacteria cause no obvious symptoms in chickens so it is impossible to tell, without testing the birds, if a flock is infected. During processing, the poultry meat can become contaminated if the intestines of an infected chicken break and the contents spill onto the carcass. In 2003 the Consumers Union found that 42% of the chicken products they purchased and tested had Campylobacter on them (Anonymous, 2003). That same year, a study conducted by the Sierra Club and the Institute for Agriculture and Trade Policy (IATP) found that 96% of the whole chickens purchased from grocery stores were contaminated with Campylobacter (Wallinga et al., 2002). Preliminary results from an ongoing project at the University of Minnesota (Jacob and Griggs, unpublished) show that just under 96% of chicken carcasses from small broiler flocks raised without antibiotics had Campylobacter bacteria present on them. In this study the carcasses were sampled during processing, just prior to entering the chill tank. Other preliminary results from the same study show that the carcasses of just over 18% of broilers from these same farms had Salmonella present on them. Only broiler carcasses from one of the twenty farms involved in the study were free of Campylobacter.

Like Campylobacter, Salmonella is carried in the intestinal tract of chickens, but it is not as common. The Consumers Union study (Anonymous, 2003) found Salmonella on 12% of the chicken they tested, and the Sierra Club / IATP study (Wallinga et al., 2002) found it on 18% of the whole chickens they tested.

Salmonella is a heartier organism than Campylobacter, and can survive longer outside of the bird. One type of Salmonella, called Salmonella Enteritidis, can colonize the ovaries of laying hens. These infected birds can lay an egg that is internally contaminated with Salmonella even though it may be clean on the outside. These eggs can appear normal and still be Grade A eggs because there is no way of knowing the eggs are contaminated without breaking them open and testing. Fortunately this type of contamination is rare and according to the CDC only 1 egg in 10,000 is internally contaminated in parts of the country where ovarian infection is most common in chickens.

Feed withdrawal prior to slaughtering is critical for preventing the spread of Salmonella and Campylobacter onto broiler carcasses. For commercial broilers, eight to twelve hours is usually recognized as the ideal amount of time for feed to be removed prior to slaughter. This allows adequate time for the intestines to empty, but is short enough to prevent a significant decrease in intestinal integrity. Producers raising broilers on pasture should also consider that the birds may be consuming grasses and insects during the ‘feed withdrawal’ time, and subsequently may have more material in their intestinal tract than would be ideal. Withdrawing feed the correct amount of time prior to slaughtering will minimize the risk of digestive tract contents contaminating the carcass during processing. The contents of the digestive tract could contain Salmonella, Campylobacter, or E. coli bacteria that are pathogenic to humans. If feed is not removed soon enough, the chicken will still have a full intestine. A full intestine will be closer to the wall of the abdominal cavity and thus closer to the blades that cut into the chicken to open its vent during processing. However, withdrawing feed too early can cause the intestines to weaken. Weaker intestines are more likely to break while they are being removed during processing. Bilgili and Hess (1997) reported that the strength of broiler intestines increased with the age of the broiler and decreased as fasting extended past fourteen hours. They also found that the intestines of male broilers were stronger than those of female broilers. Some producers remove feed the evening before broilers are sent to slaughter. Producers following this protocol should be aware of the amount of time between when feed is removed and when processing will actually begin. If the actual amount of time the broilers are off feed is exceeding fourteen hours, and intestinal breakage is a problem during processing, producers should consider removing feed later to shorten the withdrawal period.

The type of environment in which broilers are kept during the pre-slaughter fast can affect the passage of feed during that time. May et al. (1990) found that the crop emptied faster when chickens were held in a lighted room compared to a dark room. However, at eight hours after feed withdrawal the improvement was no longer significant. Summers and Leeson (1979) examined the effect of space on the emptying of the digestive tract of broilers. In their study they compared feed withdrawal in transport crates to feed withdrawal in litter floor pens and found that after twelve hours the upper tract had emptied in the chickens held in pens, but not in the chickens held in transport crates. Some producers may cage their birds to get them ready for transport to the processor at the same time they remove the feed, but this is a practice that should be reconsidered based on the data from Summers and Leeson (1979) because it could increase the risk of carcass contamination. The data from these two studies (May et al., 1990; Summers and Leeson, 1979) suggests that for optimal passage of feed broilers should be left in a lighted space that allows freedom of movement during the feed withdrawal period.

During the feed withdrawal process changes in the microbial flora of the chicken occur. Ramirez et al. (1997) found in four experiments in which chickens had been experimentally inoculated with Salmonella that a significantly (P < 0.05) greater number of crops were positive for Salmonella after eight hours of feed withdrawal when compared to the number positive for Salmonella in broilers that were not fasted. Ramirez et al. (1997) found similar results in their fifth experiment which occurred in a commercial broiler barn and did not involve experimental inoculation. In this fifth experiment they again found that significantly (P < 0.01) more crops were contaminated with Salmonella. Corrier et al. (1999) suggested that an increase in Salmonella contamination in the crop of broiler chickens undergoing a fasting period was due to their increased pecking at Salmonella contaminated litter. Hargis et al. (1995) found that during processing a chickens’ crop was 86-fold more likely to rupture than its ceca. They concluded that the crop might be an important source of carcass contamination during processing at some facilities. And Byrd et al. (1998) reported over 62% of the crops of broilers from commercial flocks were contaminated with Campylobacter after feed withdrawal. Only 25% of the crops tested prior to feed withdrawal were found to have Campylobacter in their study.

Some work has been done to find ways to reduce the amount of Salmonella present in the crop of broiler chickens. Hinton et al. (2000) orally inoculated five-week-old broilers with S. typhimurium five days prior to feed withdrawal, and tested the effect of a glucose cocktail had on the concentration of this organism in the crop of broilers during feed withdrawal. They found that a 7.5% glucose solution significantly reduced the amount of S. typhimurium in the crops of these chickens, and they suggested this was due to the increase in the amount of lactic acid bacteria and the drop in pH that occurred in the crop. Both the increase in lactic acid bacteria and the decrease in pH were statistically significant for a 7.5% glucose solution when compared to a 0% solution. In their research Barnhart et al. (1999) found that prolonged administration of 2.5% lactose in the drinking water prior to and during feed withdrawal did not significantly impact the amount of Salmonella in the crops of experimentally infected broilers. These studies show that though it may be possible to reduce the amount of Salmonella in the crop during feed withdrawal, it is difficult and more research needs to be done. In the meantime producers should consider finding ways to reduce the consumption of dirty litter by birds during feed withdrawal.

Catching and transport can be another source of bacterial contamination in a broiler flock. Slader et al. (2002) found a significant increase in Campylobacter when chickens were caught and put into transport crates. Previously negative flocks tested positive by feather swabbing after being moved into transport crates. They reported that this was a result of the transport crates being contaminated with Campylobacter, even though these crates had been washed with a commercial crate-washing system. In one instance some birds from a negative flock tested positive for Campylobacter after being caught by the catching crew but before being placed into crates. The same subtype of Campylobacter that was isolated from these birds was also found on the transport crates at that time. In this study they also found Campylobacter on some of the carcasses after processing. Rigby et al. (1980a) discovered Salmonella bacteria on the feathers of two chickens (8.7%) that had just arrived at the processing facility from a flock that had been free of Salmonella. After processing this flock three (16.7%) of the carcasses sampled were found to have Salmonella on them. The source of this Salmonella was probably the transport crates because fifteen transport crates (14%) tested positive for Salmonella before the broilers were placed into them. In another study Rigby et al. (1980b) found that 97 (86.6%) of the transport crates they tested prior to broilers being put in them contained Salmonella. Six (54.5%) of the processed carcasses tested were found to be contaminated with species of Salmonella that had not been isolated from this flock before transport, but had been found on the transport crates before this flock had been put into them. The results of these studies (Slader et al., 2002; Rigby et al., 1980a; Rigby et al., 1980b) show that bacteria from one flock of chickens can end up on chicken carcasses from a completely different flock. These results may imply that bacteria from a conventionally-raised flock could end up on products from free-range or Organic chickens if the crates or processing equipment used with the niche market birds were the same used with conventionally raised flocks.

Even after being washed in a commercial washing system transport crates are not necessarily free of bacteria and the type of material that a transport crate is made from may play a role in the risk of Salmonella transmission. Rigby et al. (1980a) tested 116 plastic transport crates after washing and found that sixteen (13.8%) were contaminated with Salmonella. In another study (Rigby et al., 1980a) this same group tested 132 plastic transport crates that had been washed and isolated Salmonella from 97 (73.5%) of them. El-Assaad et al. (1995) investigated the interactions of water temperature, sodium hypochlorite concentration, and the material of the transport crate on the reduction of Salmonella on the crate. They reported that galvanized steel was the easiest material to disinfect, fiberglass required twice as much disinfectant, and wood was not disinfected by any of the treatments they tested. These results are worth considering when deciding on the type of crates to use for transporting poultry to the processing facility and whether to use crates that are shared with other farms.

There have been reports that indicate carcass contamination can occur at various points in the processing line. For example, the feather picker can harbor bacteria on the rubber fingers, or on feathers and debris from a previous flock. Izat et al. (1988) investigated the level of Campylobacter on broiler carcasses during various steps of processing and discovered the number of bacteria on the carcasses increased significantly after picking. This was the only step in the processing line this group consistently saw a significant increase in Campylobacter levels on the broiler carcasses. But Berrang et al. (2001) also reported a large increase in Campylobacter contamination on broiler carcasses after defeathering. In one of their experiments they found Campylobacter on the skin of only one (0.8%) commercial broiler carcass prior to picking, but on the skin of 95 (79%) carcasses after picking. Based on this evidence those individuals who home slaughter should thoroughly clean and disinfect the feather picker, including the rubber fingers, after each flock of chickens is processed, or possibly even during the processing of a flock, to minimize the spread of bacteria between birds.

Campylobacter and Salmonella may be the primary two bacteria that are a food safety concern for poultry producers, but they are not the only two organisms with which producers should be concerned. One of the primary diseases that occur in small flock broiler production is coccidiosis. This disease can account for 5-10% of the mortalities in a poultry flock. Coccidiosis is caused by small, single-celled animals (protozoa) belonging to the genus Eimeria. There are a number of different species of Eimeria and each species is host specific. For example, the species of Eimeria that affect chickens are different than those pathogenic to turkeys. The parasite infects the cells lining the chickens’ intestine, destroying these cells, and creating intestinal lesions. Producers should monitor their flocks for diarrhea, bloody droppings, and decreased feed consumption because the presence of these symptoms can indicate an Eimeria infection is present. A drop in egg production in layers may also be evident. Another incentive for working to prevent coccidiosis is that it could make chickens slightly more susceptible to intestinal colonization of Salmonella (Arakawa et al., 1992). In this study they also found that chickens were most susceptible to being colonized by Salmonella at three weeks of age. This is an interesting finding given that most producers who raise their chickens on pasture move them outside at about this age. Arakawa et al. (1981) saw that concurrent infection with Eimeria may cause Salmonella infections to last longer in a chicken, possibly increasing the chance of the bacteria spreading throughout a flock. Fortunately, there are medications and vaccines for coccidiosis available.

Good management practices are the best way to prevent coccidiosis, Salmonella, and Campylobacter from becoming major problems in your poultry operation. There are a few key management areas where these diseases can be controlled. These areas include, litter management, sanitation, and biosecurity. Being thorough in these areas may mean a slight increase in the amount of labor involved in raising chickens, but the extra effort should pay for itself in improved bird performance.

Wet litter will facilitate the spread of Eimeria, and controlling wet litter is probably one of the most important ways a producer can prevent coccidiosis from becoming a problem in their operation. Good litter material should be absorbent, affordable, readily available, and easy to dispose of. The most common litter used for raising poultry is wood shavings, which meets all the criteria for good litter described above. The frequency at which litter needs to be removed and replaced will vary with each operation, the weather, and the type of litter used. All producers will find it necessary to add fresh litter on top of their old litter from time to time during the life of their birds. The frequency at which this needs to be done also varies, and will increase as the flock ages.

Producers raising chickens as free-range or pasture-raised also have to consider the cleanliness of the pasture area to which the chickens have access. Producers raising chickens in movable, open-bottom pens must realize the importance of moving these pens at least once per day. If these pens are not moved frequently the chickens will end up living in their feces from the previous day. It is also recommended that each area of pasture be used only once in three years to minimize the risk of pathogens cycling through the flocks. Producers who provide their chickens with a yard to forage in should consider rotating the area used by the chickens if the actual space used by the chickens is small and becomes heavily soiled during the life of the flock. If the birds are allowed to forage in the same yard for their entire life there is a greater chance of diseases spreading throughout the flock. If moving fences is not an option, moving the feed troughs and water dishes to a new location in the chickens’ pasture area can be an effective way to getting the birds onto clean ground.

It is important that chickens have access to plenty of clean feed and water. Feed should be stored in an enclosed location where rodents and other wild animals will not be able to access it. Bagged feed should be stored off the floor and away from walls to make it more difficult for rodents to access, and to keep it away from water condensation. Feed troughs should be kept clean of dirt and feces, and should be checked at least once per day. Feed troughs should be thoroughly cleaned and disinfected before being used with a new flock. It should also be noted that some of the ingredients and components in poultry feed will deteriorate over time. For example, the fats in the various ingredients, especially oilseeds (soybean, flax, etc.) can oxidize. Also, vitamins in the various feed ingredients can breakdown and thus become worthless. And the medications in many commercially available feeds may also deteriorate over time. Time and temperature are the two primary factors in the deterioration of feed. Feed should be used as soon as possible, and should be stored at room temperature and out of direct sunlight. Storing feed somewhere too warm, somewhere it can freeze, or in direct sunlight, can accelerate the deterioration of the various components.

Drinking water for chickens should come from a clean source such as a well or the community water source. A good rule of thumb is if you would not drink from the water source then the chickens should not have to either. Also, the containers that hold the water for the chickens should be kept clean. A contaminated water dish can help diseases spread throughout a flock of chickens. It is a good idea to empty old water from the chickens’ water dishes every morning and refill them with fresh water. It may also be beneficial to wash the water dishes with soap periodically to help keep the pathogen levels down. During warm weather it may be necessary to wash the water dishes more often than usual because many pathogens grow better at warmer temperatures. Water dishes should be thoroughly cleaned and disinfected between flocks of chickens. Allowing dishes to dry in a covered location where they will stay clean after being sanitized can be an effective means of further reducing the risk of disease spreading from one flock to another.

When flocks of multiple ages are being kept on the same farm it is a good idea to separate them from each other as much as possible. Older chickens may carry diseases to which they have built up resistance, but that could easily infect young chickens that have not acquired adequate immunity. It is a good idea to work from the younger chickens to the older ones while doing chores and after working with the older birds clothing should be changed prior to working with the young ones again. Another way of preventing the spread of diseases from older flocks to young ones is to have a separate set of footwear and coveralls for each flock. Placing a shallow tub with a disinfectant solution at the entrance to a brooder barn will also help minimize the spread of pathogens to the young flock.

Insects and rodents can transmit diseases to a poultry flock. Kopanic, et al. (1994) found that cockroaches could acquire Salmonella and spread it to other cockroaches. Producers who observe cockroaches in their poultry barns should seal cracks in the floors or walls where these bugs might enter, verify there is no feed stored or spilled on the floor, and consider placing some bait stations in the barn. Rose et al. (2000) discovered that the broiler houses they tested on commercial broiler farms were almost twice as likely to contain Salmonella if the producer had noticed rodents there. This finding should encourage producers to maintain good rodent control programs. Some ways of doing this may be to place a few traps around the perimeter of a chicken coop or yard. Rodents like shelter, so keeping the grass mowed down around a chicken coop may discourage rodents from entering it. Surrounding the coop or yard with a ring of gravel is an even more effective way of discouraging rodents because they dislike crossing an exposed gravel area where they are easily visible to predators.

Another way to prevent disease on the farm is to limit visitors. Visitors can carry diseases from other poultry flocks on their shoes, clothing, or even in their hair. Some visitors may be inevitable, and there are some simple steps that can be taken to limit the chance they bring a disease onto the farm. Shallow tubs with water and a suitable disinfectant should be available so that visitors can wash their boots or shoes before entering the farm. An alternative to this would be to have a designated pair of boots that visitors wear while on the farm, and which do not leave the farm. Disposable plastic shoe covers would be yet another way to prevent visitors from bringing diseases onto the farm. Coveralls should be made available so that visitors can cover their clothing to prevent that from being a means of disease transfer. Coveralls should not be allowed to leave the farm, and should be washed before each new flock of chickens in brought onto the farm. Visitors should not have direct contact with the chickens unless absolutely necessary, and should be kept as far from the chickens as possible. Applying these biosecurity measures should help minimize the risk of visitors carrying a disease onto your farm.

Each year many people get sick from food-borne illnesses. Food producers play an important role in minimizing the risk of people contracting these diseases. It is up to food producers to educate themselves and the buying public about how to best prevent food-related disease outbreaks from occurring. Fortunately for producers, some of the measures that can be taken to reduce these hazards are also beneficial to the health of the animals being raised and are relatively simple to implement. And as they say, an ounce of prevention is worth a pound of cure.

References are available on request
From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.