The Salmonella bacteria that cause pullorum disease are naturally present in the environment. In addition, because pullorum disease cannot be completely eradicated in breeding stock, and both vertical and horizontal transmission occur, many poultry farms have no choice but to focus their efforts on treatment. Pullorum disease is also easily masked by other conditions or complicated by secondary mixed infections. As a result, in practice, its control places more emphasis on treatment than prevention, rather than the other way around. This is an awkward situation for colleagues in the industry. Pullorum disease is an “old” disease, and most discussions of its prevention and control are old hat—no one wants to hear them. People just want an effective drug to administer. Yet over all these years, the poultry industry has still been unable to get its frequent and recurrent outbreaks under control. Lao Wang believes this is not something that can be resolved in one stroke with a wonder drug. We need to look at it from the perspective of interconnected and mutually influential factors to understand it clearly.
The incidence of pullorum disease drops markedly after four weeks of age. This is because, as chickens age, the number of lymphocytes in their bodies increases and their ability to regulate body temperature gradually improves, strengthening their resistance. However, pullets and laying hens that become infected, or whose early infections are not successfully treated, can become long-term carriers and spread the disease chronically. This poses a far greater threat to chicks than to adult chickens. Therefore, Lao Wang will focus here mainly on the prevention and control of pullorum disease in chicks.
When it comes to prevention, as a commercial contract-rearing farm, when receiving chicks you should ask clearly about the breeder flock hatchery: are the hatching eggs from your own farm or purchased externally? Were any antibiotics administered after hatching? Do you have recommendations for early medication? As a breeder flock hatchery, you have an obligation to provide farmers with this information when delivering chicks. Some farmers are unaware of their consumer rights. These are lawful rights, and it is only right that they be informed. Some breeder flock hatcheries also fail to understand their quality assurance obligations as upstream chick suppliers, and may even conceal some of the facts.
For example, with breeder flocks raised on the hatchery's own farm, the hatchery usually knows the status of pullorum disease eradication, and whether the hatching eggs, incubators, or hatchers are seriously contaminated. It also knows whether any weak or sick chicks were picked out on the day of hatching (during hatching, chicks that die soon after pipping can be picked out; most show no visible pathological changes. A small number of dead chicks may show dehydration, sunken eye sockets, dried toes, and congestion in the liver and other organs). It also knows which medications are highly effective. By contrast, when chicks are hatched from hatching eggs purchased externally, it is difficult to obtain a complete picture of all these facts. Some people may laugh and say, “Who would be that foolish? Who would admit to using externally purchased hatching eggs? Everyone would say they raised their own!” I say that is not necessarily the case. A breeder farm must have proof of the scale of its breeding stock, issued by the source of its breeding stock. This certificate, usually issued by an upstream grandparent-stock farm, is often prominently displayed on the wall of the breeder farm's office. It states the date the stock was introduced, the breed, and the number introduced. From this, one can also infer the number of chicks supplied per year or even per month: how many batches are hatched each month, and how many chicks are produced per batch? It is not difficult to determine whether the farm has enough hatching eggs of its own. One can also infer whether the hens are young or old, and whether they should be replaced (or culled, if you prefer).
Generally speaking, some externally sourced hatching eggs are supplied under long-term contracts, with stable quantities and quality. Others are purchased externally when a sudden market surge causes a temporary shortage, or to fulfill a contract when a flock of breeder chickens becomes ill and is taken out of production, requiring temporary purchases. In fact, externally sourced hatching eggs are not necessarily bad. Breeder farms with a conscience and a sense of responsibility can also supply very clean hatching eggs. Responsible hatcheries that purchase eggs externally may also collect samples from diseased chicks for bacterial culture after hatching, then conduct susceptibility testing to identify highly effective medications and know what to expect. Old Wang remembers that, many years ago, while working at a poultry breeding company, he went to a grandparent-stock chicken farm to collect parent-stock chicks. After the chicks had been loaded onto the truck, the farm's technical manager handed him a card with some hesitation. It stated that kanamycin sulfate was recommended for use after returning. Clearly, pullorum disease eradication in this batch of chickens had not gone well, and subsequent events confirmed this.
Old Wang believes that although the quality of this batch of chicks was not ideal, the other party at least had a conscience and cared about its product reputation, proactively telling him what to watch out for. Old Wang has also encountered this: for a period of time, every batch of chicks supplied by a breeder-chicken hatchery suffered from severe watery diarrhea at one day of age. The bottoms of the cardboard boxes holding the chicks were even soaked through with their watery droppings, and their feathers were wet. Farmers reported that the chicks were severely dehydrated and difficult to raise. Old Wang later learned that, because the farm had not successfully eradicated pullorum disease in its breeder chickens, it injected every chick subcutaneously in the neck with gentamicin at hatching to prevent pullorum disease in the commercial chicks. Gentamicin has a diuretic effect, which caused the severe watery diarrhea.
Wang believes that young chicks have immature kidney function, and the dose of gentamicin is high. Although it can prevent pullorum disease for a short time, severe watery diarrhea can weaken the entire flock of chicks and lead to more adverse effects later. In particular, Escherichia coli disease becomes more prevalent after two weeks, so this is not a completely reliable solution. For this reason, Wang once recommended reducing the dosage or switching to another antibiotic. After the approach was adjusted, the watery diarrhea stopped, but medication still had to be administered to the chicks after they were placed in the poultry house to prevent and treat pullorum disease.
Lao Wang believes that preventing pullorum disease requires eliminating the source. Even if this cannot be achieved immediately, farmers should be given the right to know which medicines are appropriate to use in advance, and they should also confidently assert their rights. Of course, do not make baseless, reckless suspicions or accusations against breeder farms and hatcheries; there are still producers that prioritize quality and uphold their reputations.
Another measure to prevent pullorum disease is to reduce stress factors. Among the many stress factors, two require special attention. First, promote brooding at high temperatures and avoid sudden temperature changes (for example, the house temperature on day one should be no lower than 35°C, then gradually reduced by 2–3°C within one week). Pullorum disease in chicks is usually the intestinal form, commonly known as “pasting up.” This is common in chicks under three weeks old, a period when their ability to regulate body temperature is poor and they are most sensitive to temperature changes. Low temperatures or sharp fluctuations directly disrupt digestive function, impair yolk absorption and navel healing, and make it easy for Salmonella pullorum to cause disease. Second, the handling of chicks during immunization and the vaccine itself can stress the chicks. This stress can briefly disrupt their physiological metabolism, which may cause Salmonella bacteria already present in the organs but not yet causing illness to migrate. Such migration often leads to disease. Therefore, maintaining high brooding temperatures and keeping stress during immunization mild (for example, handling chicks gently, avoiding excessive noise, providing anti-stress and immune-supporting vitamins such as VC and VE before and after vaccination, and giving glucose water to increase energy and promote liver detoxification) can help prevent pullorum disease to some extent.
Another measure to prevent pullorum disease is to purify the drinking water. Some people think that as long as medication is mixed into the feed or water, there is no need to disinfect the water itself. This is incorrect. Chickens drink water every day, and if the levels of Escherichia coli, Salmonella, and other bacteria in the drinking water exceed the limit, the chickens are continually ingesting disease-causing bacteria. If medication use, efficacy, resistance, timing, dosage, or other interfering factors change, the pathogens may take the opportunity to cause problems. In fact, Escherichia coli, Salmonella, and other bacteria can readily develop drug resistance. Some people also think that adding disinfectant to the water tank is enough to solve everything. This is also incorrect. Only a small amount of disinfectant is used, and it merely inhibits or kills some of the pathogens in the water. If the water tank, drinking-water lines, joints, and drinking equipment are not thoroughly cleaned, biofilm can develop and provide a hiding place for pathogens. It can also greatly increase the number of bacteria, beyond what the disinfectant can inhibit or kill. In other words, the disinfectant concentration in the water is insufficient to inhibit or kill the increased number of pathogens.
With the spread of green farming practices and the continuous improvement of regulations restricting, limiting, and controlling medication use, the range of available medicines is shrinking. Another measure to prevent pullorum disease is to regularly provide water containing microbial preparations instead of using medication. These include live microbial preparations and various enzyme preparations. At present, microbial preparations are not widely used in animal farming because many people still do not understand them clearly and think they are not medicines, so their use is optional. In fact, the life activities of any living animal always follow a cycle of health—suboptimal health—illness—recovery. Suboptimal health may be prolonged or brief. Microbial preparations essentially help restore balance at the boundary between health and suboptimal health. Microbial preparations are not costly and have no toxic side effects. They help regulate and cleanse the digestive tract and promote healthy digestive function; they can ensure that beneficial bacteria become established in the intestines in greater numbers than harmful bacteria and remove harmful bacteria’s endotoxins. In his clinical practice, Lao Wang used microbial preparations for many years to prevent and treat intestinal diseases in young poultry. He also conducted a comparative trial: one batch of breeding chicks was divided into two groups. The trial group received no medication, only one type of microbial preparation; the control group received medication only, with no microbial preparations. The results showed that, without medication for prevention, the trial group grew faster, had a higher healthy-chick rate, and had no cases of pullorum disease. Although the control group also had no cases of pullorum disease while receiving medication, it performed worse than the trial group on all three measures: growth, chick health, and input costs.
When it comes to treatment, people often think about what specific medicines to use, when to administer them, what dose to give, and how many times to give them. In many cases, more attention is paid to medication than to prevention. In clinical practice, treating chicken pullorum disease rather than preventing it is a reluctant choice, stemming from the mistaken belief that prevention is impossible. Treatment, meanwhile, is seen as a matter of controlling the disease with medication: if medication is not used or is stopped, the disease will inevitably occur or recur. In fact, if we improve our understanding of prevention and take effective action, treatment will no longer be so difficult. Lao Wang suggests paying attention to the following aspects:
First, Escherichia coli and Salmonella can be treated with the same medication, but ideally the medication should be highly effective against both bacteria. Escherichia coli and Salmonella are both Gram-negative bacteria, and the medications used to treat them are broadly similar. In clinical practice, treatment has generally focused on Escherichia coli. This is because, after the major viral diseases are brought under control by immunity, cases of Escherichia coli increase significantly, and its “three inflammations” symptoms are also easy to identify. As a result, Salmonella infections may be overshadowed by Escherichia coli cases, or the two may occur as a mixed infection, with Escherichia coli being the only one “blamed.” However, Escherichia coli and Salmonella still differ in their drug resistance and drug sensitivity. Escherichia coli, in particular, has more serotypes than Salmonella and is more drug-resistant. Sometimes, white diarrhea may have stopped while Escherichia coli is still present; at other times, Escherichia coli may have been controlled while white diarrhea persists. This can result in a flock becoming a carrier without showing obvious signs: some chickens may have prolonged diarrhea, delayed development, and continue shedding bacteria. Therefore, treating these two diseases with the same medication can be a case of killing two birds with one stone, but sometimes combining two medications or alternating between them over the course of a week may work better.
Second, select treatment drugs and rotate them regularly. Do not make claims such as saying that one drug is the best. For Salmonella, a genus of Gram-negative bacteria, many antibiotics are effective against a broad range of bacteria. For newly hatched chicks, drugs that are well absorbed orally may be selected to reduce the burden on the intestines, liver, and kidneys. It would be even better if a drug could prevent and treat septicemic pullorum disease, eliminate maternally transmitted Mycoplasma, and treat yolk sac infection and omphalitis. This requires summarizing and refining clinical practice. Also note that chicks under one month of age must not be given sulfonamides, as they have poor tolerance to their toxic side effects. Drug use should follow a rotation plan; even highly sensitive drugs should not be used continuously. In general, rotation once every two months is advisable. Note that accurate medication records should be kept on file for verification.
Third, the treatment schedule. Usually, administer the medication to chicks for five consecutive days after hatching to eliminate the pathogenic microorganisms they acquired from the embryo. Stop for three days to allow the medication to clear from the intestines, then administer it for another five days to continue suppressing and killing the residual microbial flora. After that, do not administer medication if there are no signs of illness; if there are signs of illness, administer medication as appropriate to the condition. This schedule is effective only when combined with proper implementation of all aspects of husbandry management.