You have all of your in-plant interventions in place, but your facility is still not in Category 1 on its salmonella test results. How can your complex improve its standing? Dr. Trisha Marsh Johnson has worked with around 30 processing plants in the USA that have had problems with their salmonella numbers and she has learned some pre-harvest interventions that can help complexes reduce their number of salmonella positives and move towards Category 1.

Johnson said that USDA ARS research has demonstrated that the salmonella isolates that show up post-chill are the same ones isolated from the pullets, breeders, hatchery residue, and day-old chicks simply magnified at each stage in live production. The isolates pulled from rodents, feed and litter prior to chick placement did not match isolates in the processing plant in the ARS study. After chick placement, the isolates from the birds could be picked up in the litter showing that it did indeed play a role in transmission throughout the flock but that it was not the source of the infection. Research has also shown that live haul cages are not the source of contamination for birds though horizontal transmission of pathogens can occur there.

Pre-harvest control

"It is important to remember that all of the interventions available only work when preventing infection of an uninfected bird," Johnson said. "They are not capable of removing salmonella from a bird that is already positive. An individual infected bird will begin shedding salmonella during hatch. The process of pipping can aerosolize enough salmonella to infect an entire hatch cabinet. From there the infected chick begins to shed salmonella in the feces. As its neighbors begin to preen themselves after hatch or begin pecking at the meconium in the chick boxes, horizontal transmission begins.

"The rationale behind on-farm bacterial control is quite simple," Johnson said. "Once a contaminated bird is inside the plant, there is little a plant can do to remove bacteria like salmonella from that individual carcass. The plant can only work to prevent that carcass from spreading bacteria to other carcasses around it. However, if you reduce the number of bacteria the bird comes in contact with on the farm, you can help to prevent that bird from carrying salmonella into the processing plant. Extensive epidemiological research done by the USDA and several poultry integrators indicate that on salmonella positive farms, only 10 to 15 percent of the birds are intestinally-infected with salmonella while 50 to 75 percent of the birds in that salmonella-positive flock are carrying salmonella on their skin and feathers."

Start with the pullets

If you can place chicks or poults that are basically negative for salmonella, then you can keep most of them negative, according to Johnson. Pullet chicks are delivered from the primary breeders with salmonella incidence rates below the detectable level. Johnson said, "Pullet placements are probably less than 1 percent positive at placement, but the salmonella is still there, even if you can't detect it." Focus should be placed on keeping the 99-plus percent of pullet chicks that arrive on the farm negative for salmonella.

Johnson recommends acidifying the drinking water for pullets throughout their time in the pullet house, since pullets are on restricted feeding programs. Water acidification to a pH of 3.5 or less will selectively promote gut colonization with good healthy bacteria while suppressing salmonella in the crop.

The salmonella serotype profile found in the plant will generally match that of the breeder flock, which will reflect what came in from the grandparent flock. Johnson said that this serotype signature can be altered by using killed autogenous vaccines on the parent flocks. Live salmonella vaccines can be used on the day old meat birds as well.

On the growing farm

Based on work Johnson has done with numerous processors, she said that if you are placing day old chicks with greater than a 5 to 10 percent rate of salmonella positives, then it is really hard to keep the flock down at an incidence rate that will give you the results that you want at the end of the chiller. If there is only one bird in 100 infected, then the rate of spread is slow, but if 50 out of 100 are infected, than horizontal transmission occurs rapidly.

Salmonella positive chicks or poults shed salmonella fairly heavily the first week on the farm. Their flock mates will be very susceptible to colonization that first week as well. Because of this, Johnson recommends acidifying the drinking water for the first week to 10 days of a broiler or turkey flock and the last 24 hours during feed withdrawal. "Research has shown that providing mineral and organic acids in the drinking water greatly reduces post-harvest crop contamination with salmonella," Johnson said. She said that it is important to use acid any time the normal crop or gut flora are disrupted. This occurs most commonly when the birds are off-feed, whether intentional or not, or when given therapeutic antibiotics. During any feed withdrawal of more than 6 hours, the normal lactic acid producing bacteria in the crop and gut begin to die off and crop and gut pH increases. This allows for the survival and proliferation of salmonella that is already in the gut or that the bird is exposed to during this time. Growers should acidify the drinking water anytime the bird is exposed to a stressor, like moving from brooder to grow-out house in turkeys or from pullet to layer house in breeders.

Acidifying litter treatments can also help control salmonella numbers in the litter, according to Johnson. A low pH, high sodium environment in the litter will favor growth of lactic acid producing bacteria. Because negative birds are most susceptible to colonization in the first seven days, brood chamber application of litter acidifiers is important. Because the highest shedding of salmonella in broilers occurs from days 18 to 21 of age, the other part of the house can't be ignored either.

Getting results

Johnson said that if your salmonella positive birds are running at less than 5 percent, than most of your amplification is taking place in the growing house. But, if the incidence is running 25 percent or more, then you will need to start your work in the hatchery and breeder operations. She said that if your problem is in the growing houses, then you can expect to see results after one full growing cycle is completed, but if your problem is at the breeder and hatchery level, it can take four to six months to see major improvements.