When a poultry company exceeds the Salmonella standard set by the USDA, the initial reaction is to place blame on the plant employees. Various companies have spent enormous amounts of time and money attempting to reduce Salmonella levels on finished carcasses by making changes in the plant. Unfortunately, this is not always successful. Numerous factors during breeding, hatching, growout, and transportation (chick and broiler) can directly impact the level of Salmonella on the finished product.
Actions that can be taken to control Salmonella pre-harvest were outlined in the article The Next Step which appeared in the September issue of WATT PoultryUSA magazine (which can be viewed in the digital edition at September 2007 WATT PoultryUSA or online at Pre-Harvest Salmonella Reduction: The Next Step).
The breeder chickens have been a cause of concern for the poultry industry for many years with regard to Salmonella. Salmonella may be transferred on the surface of the egg shell due to fecal contamination during laying, or it may be encased within the egg. Cox and others found that Salmonella could be found in the reproductive tracts of roosters and in hen sperm storage tubules. These findings indicate that roosters may be infecting hen’s reproductive tracts during insemination. Thus, to prevent vertical transmission of Salmonella, many companies have instituted a vaccination program. These programs are showing some positive benefits in decreasing Salmonella populations within the breeder chickens of some companies; however, other companies have reported that, even though their breeders have been vaccinated, 100 percent of the chickens entering the plant are contaminated with Salmonella on a routine basis. This may be explained by the fact that the vaccines, although directed against a broad variety of Salmonella serotypes, do not work as well with some of the serotypes. In areas where the resistant serotypes exist, vaccines for the breeders may not be a viable option.
In some European countries, all breeder flocks are tested for Salmonella. If the flock is positive, it is slaughtered and the eggs are not used. This has dramatically reduced Salmonella populations in the broiler chickens. However, due to the sheer scale of the industry in the USA, this approach is seriously impractical.
Another approach that many European countries use is competitive exclusion. The idea is that by feeding the chickens populations of “good bacteria”, these good bacteria will colonize the intestines of the chicken and fill up all of the parking spaces. Then, when Salmonella is ingested it: 1) does not have anywhere to park, and 2) bacteriocins (bacterial antibiotics) produced by the good bacteria will kill the Salmonella. The cultures used in these countries are generally undefined. That is to say that the bacterial species in the culture are not defined and identified. The U.S. Food and Drug Administration will not allow these cultures to be used in the USA. Thus, very few cultures are used and sold in the USA. These cultures have not been widely accepted by the industry. In Europe however, the undefined cultures have been demonstrated to be successful at reducing Salmonella.
To reduce the prevalence of Salmonella on poultry carcasses during processing, intervention strategies should be implemented during the hatching phase of poultry production. Salmonella spp. may be found in the nest box of breeder chickens, cold egg-storage rooms at the farm, on the hatchery truck, or in the hatchery environment (Cox et al., 2000). These bacteria may then be spread to fertilized hatching eggs on the shell, or in some cases, may penetrate the shell and reside just beneath the surface of the eggshell.
Research has demonstrated that contamination of raw poultry products with Salmonella spp. may be attributable to cross-contamination in the hatchery from Salmonella infected eggs or surfaces to uninfected baby chicks during the hatching process. Cox et al. (1990 and 1991) reported that broiler and breeder hatcheries were highly contaminated with Salmonella spp. Within the broiler hatchery, 71 percent of eggshell fragments, 80 percent of chick conveyor belts swabs, and 74 percent of pad samples placed under newly hatched chicks contained Salmonella spp. (Cox et al., 1990).
Cason et al. (1994) reported that, although fertile hatching eggs were contaminated with high levels of Salmonella typhimurium, they were still able to hatch. The authors stated that paratyphoid salmonellae do not cause adverse health affects in the developing and hatching chick. During the hatching process, Salmonella spp. is readily spread throughout the hatching cabinet due to rapid air movement by circulation fans. When eggs were inoculated with a marker strain of Salmonella during hatching, greater than 80 percent of the chicks in the trays above and below the inoculated eggs were contaminated (Cason et al., 1994). In an earlier study, Cason et al. (1993) demonstrated that salmonellae on the exterior of eggs or in eggshell membranes could be transmitted to baby chicks during pipping.
Salmonella may persist in hatchery environments for long periods of time. When chick fluff contaminated with Salmonella was held for 4 years at room temperature, up to 1,000,000 Salmonella cells per gram could be recovered from these samples (Muira et al., 1964). Researchers have demonstrated a link between cross-contamination in the hatchery and contaminated carcasses during processing. Goren et al. (1988) isolated salmonellae from three different commercial hatcheries in Europe and reported that the same serotypes found in the hatcheries could be found on processed broiler chicken carcass skin. Thus, proper disinfection of the hatchery environment and fertile hatching eggs is essential for reducing Salmonella on ready-to-cook carcasses. Suggestions for elimination of Salmonella in the hatchery include:
1. Install a disinfectant fogging system or electrostatic spraying system in the hatchery plenum, setters, and hatchers that are linked to a timer system.
2. Spray disinfectant every 30 minutes during setting and hatching to prevent cross-contamination.
3. Thoroughly clean and sanitize setters and hatchers regularly using documented sanitation standard operating procedures (SSOP’s).
4. Regularly monitor eggshell fragments, chick paper pads, and chick dander from the bottom of the hatching cabinet for Salmonella.
Figures 1 and 2 demonstrate the efficacy of electrostatic spraying on coating a black ball (model for an egg) with a disinfectant. Figure 3 indicates that disinfecting the eggs with electrolyzed oxidative (EO) water in a U.S. Poultry and Egg Association funded study had no impact on hatchability. Figure 4 shows the data obtained during that study for prevention of colonization of chickens using electrostatic application of EO water during the hatching process.
The modern broiler chicken has been bred over the years to be a veritable “eating machine.” During growout, broiler chickens eat approximately every four hours. Frequent eating is advantageous because birds that eat this frequently gain weight and put on edible muscle rapidly. This attribute may be considered a disadvantage for maintaining the sanitary quality of the bird during processing. At the end of the growout period, prior to catching the birds and cooping them for transportation to the processing plant, the feed is removed from the birds for a period of approximately 3 to 7 hours. During this time, birds become hungry and begin to search for food. Because there is no food available to them in the feeders, they begin to search for feed on the floor, which may be contaminated. This activity has been demonstrated to significantly contribute to the level of Salmonella on processed carcasses (Byrd et al., 2001). Studies have shown that many birds entering the processing plant have high levels of Salmonella in their crops as a result of this litter pecking (Byrd et al., 2001).
Salmonella in the crops of chickens that have consumed litter may be spread from carcass to carcass during the crop removal process (Hargis et al., 1995, and Barnhart et al., 1999). During cropping, the cropper piston is inserted into the vent area of the carcass and continues through the entire carcass, spinning as it goes. The piston has sharp grooves on the end of it that pick up the crop and wraps the crop around the end of the cropper piston. As the piston moves through the neck opening, the cropper piston comes in contact with a brush that removes the crop from the piston. Then, the piston, while spinning, goes back through the entire carcass. If the crop breaks during this removal process, the contents leak onto the cropper piston and are transferred to the interior and exterior of the carcass, possibly spreading Salmonella.
Studies have been conducted by Dr. Allen Byrd of the USDA - Agricultural Research Service (ARS) in which the crops of live birds were filled with fluorescein dye. After thirty minutes, the birds were processed. By examining the carcasses at different stages of processing under a black light, crop contents that were transferred to the inside or outside of the carcass could be clearly visualized. These studies have shown that commercial croppers result in a large amount of contamination of the inside and outside of the carcasses. Thus, efforts should be made to control Salmonella in the crop prior to the crop removal process.
Some companies have been successful at controlling Salmonella in the crop by acidifying the bird’s drinking water during the feed withdrawal process. Acetic, citric or lactic acids and Poultry Water Treatment (PWT) have all been used to acidify the crop to the extent that Salmonella are unable to survive. Byrd et al. (2001) found that lactic acid was most effective and that 0.44 percent lactic acid in the waterers of broilers during the feed withdrawal period reduced Salmonella contaminated crops by 80 percent. This effect carried over to the pre-chill carcasses on which the prevalence of Salmonella was reduced by 52.4 percent (Byrd et al., 2001). When acidifying drinking water using lactic acid, it is best to gradually expose the birds to higher and higher levels of acid in the water the week before birds are to be caught. The key is to make the lactic acid concentration as high as possible while ensuring that the birds continue drinking the water. Suggestions for elimination of Salmonella in the crop prior to processing are as follows:
1. Apply lactic acid to drinking water of the chickens before the feed withdrawal period.
2. Begin by applying small amounts and gradually increase levels until they reach 0.5 percent (0.64 oz. of lactic acid/gallon of water).
3. Occasionally have the QA employees check the pH of the crops of birds at the plant to insure that they are being acidified.
Another popular method for reducing Salmonella in broiler chickens is to spray the chicks with a live vaccine in the hatchery. The two main companies that produce these vaccines are Fort Dodge and MeganVac. Using vaccines, companies have observed Salmonella reductions of 20 to 50 percent. As with breeders, European countries often use undefined competitive exclusion cultures. In Europe the growers have found that undefined competitive exclusion cultures have been demonstrated to be successful at reducing Salmonella.
Prior to evisceration, carcasses should be evaluated to determine if the birds have undergone proper feed withdrawal. By examining the abdominal cavity to see if it is concave (small amount of feces in the intestines) or convex (large amount of feces in the intestines), it is possible to determine if the birds have been withdrawn from feed long enough.
Moreover, the intestinal tracts on the intestines hanging from the birds after evisceration should be flat and not full of feces or bloated with gas (Northcutt et al., 1997). In the processing plant, birds held off feed for extended periods may exhibit a higher incidence of contamination with pathogens as the result of cross-contamination from bird to bird during transport due to loose droppings. These birds may have intestines that are distended with gas which, if nicked during evisceration, may explode and disperse contents onto the carcass, other carcasses, or processing machinery. Extended periods of feed withdrawal also cause the tensile strength of the intestines to become weak (Northcutt et al., 1997). Weakness increases the propensity for them to be torn during evisceration.
If birds are not held off feed long enough (< 8 hours), the intestines will be full of digesta (Northcutt et al., 1997). If full intestines are nicked during evisceration, it is likely that contents will be spread to the inside or outside of the carcass, to other carcasses, and to processing equipment. Also, if pressure is applied to the outside of a bird with full intestines, the contents may come out of the vent and spread onto the carcass. Immediately after venting, if the colons are full of material, then the contents will leak onto the carcass, especially if any line jerking or swinging occurs. Insufficient feed withdrawal time is perhaps the most important factor in meeting the zero tolerance standard for contamination on carcasses entering the chiller. Reprocessing levels as high as 75 percent and line speeds as low as 20 birds/minute have been reported in plants due to excessive contamination as a result of insufficient feed withdrawal times.
Conventional cage-dump systems used in the poultry industry are very difficult to clean and sanitize. If transportation coops are to be cleaned, they must be thoroughly washed and sanitized. Dry excreta should be removed before washing if possible. Some companies have implemented rinsing systems that do not thoroughly clean excreta off coops. This rehydrates the excreta, allowing Salmonella to proliferate. All of the environmental conditions (nutrients, pH, moisture, and temperature) that Salmonella require to multiply are available if the company simply rinses the coops. Thus, if disinfection systems are used, it is best to ensure that they are capable of thoroughly removing excreta prior to sanitizing the coops.
Reducing Salmonella on fully processed, ready-to-cook carcasses requires a comprehensive approach that includes the entire integrated broiler operation. Efforts should be made during breeding, hatching, growout, and transportation to reduce Salmonella prior to processing. All emphasis should not be placed on the processing plant, nor should all of the blame be placed there. Introducing the interventions described above may have a tremendous beneficial effect in terms of reducing Salmonella on processed carcasses.