Analysis and Reflections on the Disease Development Trends of Laying Hens and Broilers

At present, with the scaling up and intensification of poultry farming, poultry diseases are gradually tending toward younger age of onset and increasing complexity, especially diseases of laying (and meat) chickens, which are becoming more and more complex. Once an outbreak occurs, it is very difficult to eradicate, greatly reducing economic returns. The following is a summary of the new characteristics of disease epidemics in laying (and meat) chickens during production, for the reference of fellow farmers.

I. Tendency toward younger age of onset

Early disease onset: respiratory symptoms appear as early as 3-5 days of age in meat poultry, manifesting as slight nasal shaking and coughing, especially after the first vaccination with the small triple vaccine, due to immune response and stress stimulation of the respiratory tract, the respiratory symptoms worsen. In some flocks, before there is time to administer the Newcastle disease vaccine, Newcastle disease breaks out at 6 days of age, and in some even earlier, with very typical symptoms; combined with delayed treatment, the mortality rate rises day by day. In some cases, infectious bursal disease breaks out at 7-9 days of age, accompanied by respiratory and enteritis symptoms. Since the body has just lost the protection of maternal antibodies and has not yet been immunized, treatment is very tricky, and the mortality rate is often very high; even if cured, it is very unfavorable for later growth.

This is inseparable from the quality of breeder chickens: due to unscientific rearing, irrational disease treatment and drug abuse, breeder chickens may carry one or even several diseases continuously throughout their lives. In particular, infection with Mycoplasma, E. coli, nephropathogenic infectious bronchitis, leukemia, etc., has an imaginable impact on hatching eggs. The chicks that hatch carry bacteria and viruses, and their later growth and development is far from optimistic. Therefore, it is recommended that farmers must purchase chicks from SPF breeder farms.

II. Analysis of the reasons for increasing complexity

1. Disinfection inside and outside the chicken house and of equipment is not strict and is highly arbitrary: after a batch of chickens is marketed, the chicken house should be left empty for at least two weeks. In the week before chicks arrive, all items inside and outside the house unrelated to brooding should be removed, walls and floors washed, doors and windows repaired, and disinfectant sprayed. Five days before chicks arrive, drinkers, feed buckets and other supplies should be placed inside the house, doors and windows closed, and fumigation disinfection with formaldehyde (42 ml formaldehyde per cubic meter of space, 21 g potassium permanganate) should be applied, kept sealed for 24 hours, then doors and windows opened for ventilation for 24 hours. But now farmers, for convenience, rarely go to all this trouble, and instead use "smoke bombs" and the like produced by some manufacturers to replace formaldehyde fumigation disinfection. For them, disinfection is a routine matter, just going through the motions, since no immediate effect can be seen anyway. Some farmers simply spray with only one or two disinfectants. Because the concept of disinfection is weak, pathogens persist in the chicken house for a long time. Over time, when bacteria multiply to a certain level, chicks become ill very early and it is very difficult to eradicate.

2. Immunization is unscientific and methods are non-standard

For example, at the first immunization against infectious bursal disease, it is often the case that not immunizing would have been better. Once immunized, the flock becomes depressed, with obvious respiratory and intestinal symptoms, accompanied by death. During this period, large amounts of drugs against intestinal and respiratory infections are used, with varying results, and the mortality rate begins to rise. Considering that the flock was in the incubation period of infectious bursal disease at the time, immunization caused low body resistance, and the pathogen could infect and cause disease through the respiratory tract at any time, producing a series of symptoms. It is precisely because immunization during the incubation period occurs when body resistance is low that the effect of infectious bursal disease vaccination is very poor; after vaccination, respiratory and intestinal symptoms instead become more severe. At this time, the bursa of Fabricius, an immune organ, has already become diseased, and then a series of symptoms appear. At this point, various Chinese and Western medicines for respiratory, intestinal and anti-infectious bursal disease have no significant effect. Eye-drop or mouth-drop administration for the first immunization against infectious bursal disease is the scientific immunization method, but in reality people often use drinking water for the first immunization to save trouble, and the result is also one of the reasons for the above situations. Even more absurd is that when immunizing against fowl pox, instead of wing-web stabbing, drinking water is used, and it is often administered simultaneously with strain I. Strain I is not injected but given in drinking water, seriously violating science. Infectious laryngotracheitis vaccine is the vaccine that farmers dread most. Cloacal brushing or eye drop is the most advisable method, but people, fearing the stress caused by immunization, use drinking water immunization. Some farmers do use the cloacal brushing method, but the operation is seriously wrong and the vaccine is not brushed into the cloaca at all, failing to achieve the proper immune effect, so that once an outbreak occurs later, it is very difficult to cure. For commercial laying hens after the peak laying period, because Newcastle disease antibody levels are low or uneven, Newcastle disease vaccine needs to be revaccinated at regular intervals, generally using strain I, strain IV or co-30 immunization. Theoretically, the most reasonable way to use strain I is intramuscular injection, but in reality people often use drinking water, and the dose is frighteningly large, with strain I given at 5-6 times the dose in drinking water every month. The correct method for Newcastle disease revaccination of commercial laying hens after the peak laying period should be: every one or two months, alternate immunization with strain IV or co-30 by drinking water and spraying, with the immunization dose depending on local conditions. Why use alternating immunization with strain IV and co-30 by drinking water and spraying? The reason is that drinking water immunization is most easily absorbed by the digestive system, and its protection rate for the respiratory system is almost zero. Strain IV can raise Newcastle disease antibody levels in the body, while co-30 can make antibody levels more uniform; alternating the two can raise antibody levels on the basis of uniformity, thereby achieving the purpose of disease prevention. Also, during intramuscular or subcutaneous injection immunization, the needle should be changed for each chicken, avoiding the unscientific and irrational practice of using one needle for the whole flock.

3. The impact of nutritional levels on the prevention and treatment of poultry diseases

For a long time, people have often focused only on the impact of nutritional levels (protein, fat, vitamins, minerals, etc.) on poultry production performance, while ignoring their role in disease prevention. In recent years, research in this area has become a hot topic in animal science research. Preliminary studies at home and abroad show that nutritional deficiency or excess can lead to immunization failure in poultry and increase disease incidence, thereby affecting the return on farming investment.

For example, chicks are prone to infectious nephropathogenic infectious bronchitis in the early stage. Relief methods: first, raise the house temperature by 1-2 degrees C; second, reduce the protein level in the diet, for example by adding crushed corn to the feed; third, provide symptomatic treatment and add medication. If one does not pay attention to the impact of nutritional levels on the prevention and treatment of chicken diseases, and blindly increases the drug dosage while ignoring this, the large-dose use of drugs will instead increase the burden on the kidneys and fail to improve the body's metabolic balance in time, making the disease worse with treatment, eventually leading to mortality and delaying the best period for treatment. Also, when chickens have an outbreak of gout, while treating with drugs, attention must be paid to reducing protein in the feed. In addition, during respiratory and intestinal diseases in the flock, attention must be paid to vitamin supplementation to compensate for what the body has lost.

4. There are many factors affecting outbreaks of poultry diseases, among which feeding and management levels (temperature, humidity, stocking density and the content of harmful gases produced by metabolism, etc.) are daily work that cannot be ignored. The most inconspicuous yet most important task in daily work is manure removal, which often fails to attract people's attention. Theoretically, manure should be removed once a day and disinfection carried out once a day, but in reality very few do this, giving diseases a great opportunity to invade. Most farmers remove manure once a week to once every half a month. In winter it is somewhat better, but in summer, because chickens drink a lot of water, the manure is very thin, and the humidity in the chicken house can be imagined, with a foul smell and flies everywhere. As for harmful gases, especially in winter when stoves are burned inside the chicken house, ventilation and warmth retention cannot be well combined, resulting in a strong ammonia smell and a very poor rearing environment. For broiler chicks brooded on litter, farmers, seeking cheapness, do not change the litter batch by batch, but pile one batch on top of another, so that pathogens cannot be effectively killed and instead survive long-term in the chicken house. When the opportunity matures, the flock can become ill again. This is also one of the reasons why coccidiosis is difficult to eradicate under litter rearing.

III. Reflections on current disease prevention and treatment

1. Understanding of respiratory diseases

At present, two types of Mycoplasma infection are relatively difficult to eradicate: one is vertical transmission; the other is vaccine contamination. If the initial medication is selected in a targeted way, or if special drugs for preventing respiratory infections are used after immunization, the treatment effect is relatively reliable. Infectious coryza is also a relatively stubborn and difficult-to-eradicate infectious disease, with a very high recurrence rate, which is closely related to poor chicken house environments. It is recommended that while treating respiratory diseases, drugs for treating E. coli disease be used in combination. Because the concentration of drugs reaching the air sacs is very low, when treating airsacculitis it is best to use aerosol administration, because aerosol administration allows drugs to reach and act directly on the surface of the air sacs through the respiratory tract. Intramuscular injection can also be used to rapidly raise the drug concentration in the blood and act quickly on the air sacs. For the whole flock, a treatment method combining Chinese and Western medicines should be adopted, with Chinese medicines used to relieve cough, resolve phlegm, calm panting and improve body immunity. In addition, cod liver oil has a strong repairing effect on the respiratory mucosa, and its adjunctive therapeutic effect on respiratory diseases cannot be ignored.

2. Understanding of E. coli in chicks

There are two causes of E. coli infection in chicks: one is vertical transmission; the other is cross-infection. For the first type, one can raise the house temperature, as 33-34 degrees C is the optimal temperature value for yolk absorption, and also carry out regular drug prevention. For the second type, one can disinfect the environment inside and outside the chicken house, combining drinking water disinfection and spray disinfection, and also pay attention to drug prevention. Remember to use highly sensitive antibacterial drugs during prevention. Once implemented, the effect at the time is very significant; when the disease breaks out later, curing it is extremely difficult.

3. Vaccine selection is very important

Formal brand products should be selected, preferably SPF vaccines. In addition, one should reasonably and scientifically choose whether to use combined vaccines or single vaccines according to local disease prevalence, adopt the correct inoculation method and immunization dose, consult the technical personnel of the vaccine manufacturer, and use the optimal dose and timing of the vaccine. One must not blindly increase or reduce the dose. Third, attention should be paid to filling the immune blank period with drugs, which can not only prevent virus invasion during the immune blank period, but also help improve body immunity and antibody titers and reduce immune reactions. Generally, antiviral Chinese medicines are used for drug filling.