Common diseases of chickens. Treatment of respiratory mycoplasmosis in poultry

G.V. Beginin, chief veterinarian PF "Gayskaya"

The epizootic and economic well-being of poultry enterprises largely depends on timely diagnosis and measures specific prevention against infectious diseases, which include Gumboro disease.

Gumboro disease at the Gayskaya poultry farm in the Orenburg region was first registered in November 1995 among 45-day-old chickens of the Zarya-17 cross. Clinically, the chickens were observed to be lethargic, lack of appetite and watery diarrhea. Characterized by ruffled plumage and at times muscle tremors.

During the epizootic period, the disease manifested itself in 6 workshops of the poultry farm. The disease was observed simultaneously in different poultry houses and the number of sick chickens in some poultry houses reached 50%, and in others – 10–20%. Chicken mortality in some workshops was more than 30% within 7–10 days. The maximum death of birds was noted on the 3rd–5th day of illness and decreased in the next 4–5 days.

At autopsy, dry subcutaneous tissue, pinpoint or diffuse hemorrhages in the pectoral and femoral muscles were noted, the bursa of Fabrice was enlarged 2–3 times, hyperemic or with hemorrhages (in 30–40% of cases), sometimes there were fibrin deposits in its cavity. Kidney lesions were noted in 40% of the examined corpses.

They were enlarged, with hemorrhages, and there was an accumulation of urates in the ureters. The diagnosis was made on the basis of epidemiological data, clinical signs, pathological changes and the results laboratory research, held at VNIVIP.

Since the outbreak of Gumboro disease, different vaccines have been tested at the poultry farm, varying in their effectiveness due to the presence of maternal antibodies and changes in poultry crosses.

Initially, against the background of low passive immunity, the double use of the vaccine from the “VNIVIP” strain made it possible to ensure high safety and productivity of poultry in unfavorable conditions. After a long period of successful prevention clinical signs and lesions in the bursa of Fabricius during autopsy of dead birds appeared in vaccinated livestock upon reaching 35–37 days. Then the disease spread to other buildings where birds of an age susceptible to the IBD virus were kept.

An analysis of the reasons for the failure of vaccine prophylaxis showed that by that time the young animals accepted for rearing had high levels of maternal immunity, since they were obtained from hyperimmunized laying hens, and in the batch of chickens where a specific death was observed, there were violations of the vaccine application technique, in some In some cases, the poultry house housed chickens of different ages with different immune backgrounds.

It was possible to stabilize the epizootic situation on the farm with the help of a vaccine from the BG strain. With the transition to a new vaccine clinical manifestation diseases were not observed, but they encountered such problems as atrophy of the bursae of Fabricius, retardation of poultry in growth and development, a high percentage of their rejection, a low percentage of commercial pullets and kidney pathology in replacement young stock caused by an increased content of uric acid salts in the ureters.

After changing the poultry population to the Rhodonit cross, in which the parent flock was not vaccinated with the inactivated Gumboro vaccine and the level of maternal antibodies in the RDP of day-old young animals did not exceed 30%, they began to use a vaccine from the KBK strain produced by Biovet LLC (St. Petersburg ). The vaccine was administered once into the upper third of the neck of day-old chickens subcutaneously in a volume of 0.2 ml. To dilute the vaccine, we used Marek's disease vaccine diluent produced by the Kursk biofactory.

The effectiveness of the vaccine from the KBK strain was assessed by the level of specific antibodies in the RDP, bursal index and titers to the Newcastle disease virus.

In the blood serum of vaccinated chickens 25–30 days of age positive reaction in RDP was noted in 80–100% of cases. The bursal index at the age of 30 and 40 days was at least 3.5. The bag had a natural color and without visible signs defeats. Group immunity against Newcastle disease 15 days after revaccination was 6.42 log2, which indicates a pronounced immunological reaction of the bird to the vaccine. Observations have shown that the vaccine from the KBK strain does not cause immunosuppression; the growth and development of poultry complied with zootechnical standards. Safety among young animals during the period of use of this vaccine increased by 5%, the yield of commercial pullets was 97% with high uniformity of the herd.

Some batches of chickens were vaccinated against Marek's disease and Gumboro disease simultaneously. Performance indicators for separate and joint immunization against Marek's and Gumboro's diseases did not differ significantly.

In 1998, another change of livestock was carried out to the “Loman White” cross, where the prevention of Gumboro disease was carried out according to the program of the “Loman” company (Germany) and passive immunity in the first days of life, according to ELISA data, was 1: 5000 and higher. In the current situation, it was necessary to change the vaccine and adjust the existing disease prevention program.

Taking into account previous experience in disease prevention and positive reviews colleagues on the prevention of Gumboro disease using an inactivated vaccine on young birds, it was decided to vaccinate with this vaccine from the “52/70 M” strain (produced by Biovet LLC). At the same time, a comparison was made with a live vaccine from the “BG” strain and a scheme for using the killed vaccine was worked out to develop tactics for preventing the disease in the future.

To do this, one group of chickens was vaccinated with an inactivated vaccine at 10 days according to the instructions for using the drug; the second group was vaccinated at 16 days with an inactivated vaccine; the third and fourth groups of chickens were simultaneously vaccinated with inactivated and vaccine from the “KBK” strain at 10 and 16 days, respectively; chickens of the fifth group were vaccinated with a vaccine from the “BG” strain at 7 and 17 days.

The effectiveness of vaccines and their application schemes was judged by the well-being of the farm against Gumboro disease, general safety, productivity, business output of replacement young stock and by the results of blood serum studies for the presence of specific antibodies in the RDP of 30-, 40-, 50- and 60-day-old chickens. At the same time, the level of post-vaccination immunity against Newcastle disease was studied, and the bursal index was determined at different periods of poultry rearing.

Comparative production indicators for raising poultry according to the specified vaccination schemes are given in Table No. 1.

Table 1
Performance indicators of chickens vaccinated with different vaccines against IBD

Indicators	Group numbers
Number of goals
Average daily weight gain, g
weight 1 head. when transferred to 112 days, g
% business pullet
Safety, %
Uniformity, %
% of egg laying in 150 days.
Culling, %

From the presented data it is clear that the vaccines used against Gumboro disease according to the indicated schemes provide complete protection of chickens from the field virus. Administration of inactivated vaccine to chickens does not cause adverse reactions local and general. Chickens vaccinated with an inactivated vaccine at different times separately and in association with a live vaccine have the highest rates of safety (up to 99.4%), average daily weight gain that meet regulatory requirements, a high percentage of commercial pullet yield (97.4%), and a low percentage of rejection (0.49%) and high uniformity of the herd (88.3%).

The dynamics of serological indicators of the reaction to the introduction of vaccines indicates that the most active group immunity was established in group IV of chickens simultaneously vaccinated live and inactivated by vaccines at 16 days. The arithmetic mean titer of serum in the RDP was 3.8 log2. High performance bursal index (more than 5.2) were noted in I -IV groups, while in the V group low performance bursal index was observed starting from 30 days of age.

CONCLUSION
The effectiveness of preventing Gumboro disease is closely related to the type of vaccine, compliance with the rules for its use, and the presence of maternal antibodies, which negatively affect the development of post-vaccination immunity, both when administered live and inactivated vaccines.

The vaccine from the KBK strain is effective against a low immune background of passive antibodies. The use of a vaccine from the “BG” strain helps to stop the infection, but causes damage to the bursa and kidneys, which leads to a decrease in the overall safety and productivity of the bird.

High safety and productivity in our farm conditions was achieved with joint vaccination with inactivated and live vaccines against IBD at 16–18 days.

Prepared based on the materials of the “Vth International Veterinary Congress on Poultry Farming” for the website

Mass breeding of chickens on farms requires compliance with many rules and regulations. Highly productive and healthy birds are the result of daily care for their health, because today there are many diseases with a rapid rate of development and a high mortality rate. One of them is Gumboro disease: let’s look at its features and the main methods of control.

What kind of disease is this

Gumboro disease, or infectious bursitis, acute viral disease chickens, the first appearance of which became known in 1962 in the city of Gumboro (United States of America). Today it affects livestock not only in America, but also in other countries of Europe and Asia.

Economic damage

For poultry farmers, the losses are significant and are calculated not only in the number of dead livestock, but this is 10–20% of the total flock. Sometimes deaths occur in 50% of total number sick chickens: it all depends on the age, breed and conditions of their keeping.

A large percentage of culled carcasses, which lose their attractiveness due to multiple hemorrhages and exhaustion, also bring losses.

The disease also has many indirect negative factors. Firstly, it greatly weakens the herd, making it susceptible to many other infections, and secondly, it significantly reduces the effect preventive vaccinations, thirdly, it negatively affects the productivity of the livestock.

Important!There is still no way to cure infectious bursitis. Most effective method combating the disease - timely vaccination.

The causative agent of the disease

The causative agent of the disease enters the bird's body through the mucous membranes. It is able to withstand temperatures up to +70°C for half an hour, and is resistant to alkalis (pH from 2 to 12) and acids, as well as lipid solvents. The causative agent of Gumboro disease can survive in chicken droppings for up to four months.

Only disinfectants can quickly destroy virus cells:

formalin;
iodine derivatives;
chloramine

This virus does not have antigens and is classified as a reovirus. For a long time Bursitis virus was classified as an adenovirus. For some time after the disease was identified, it was believed that infectious bursitis and infectious bronchitis were caused by the same pathogen.

Only chickens are susceptible to the infectious bursitis virus, although it is believed that the disease also affects sparrows and quails.

Epizootological data

The main risk group is reproductive farms that house individuals of different ages. The main source of bursitis is chickens infected with the virus. Most often, the disease has an acute and subacute course; less often, bursitis passes without symptoms.
The virus quickly affects the entire herd. It is noteworthy that Gumboro disease is not observed in young birds up to two weeks of age and in adult birds. Even if they are infected artificially, they will remain immune to the virus. Chicks suffer from bursitis between the ages of 2 and 15 weeks. Chickens aged 3 to 5 weeks are most susceptible to it.

Did you know? - chickenoriginally from South America,which lays blue and green eggs. The reason for this phenomenon is increased content in the chicken's body there is a special bile pigment that colors the shell.

Keeping sick and healthy birds together, contaminated food and water, droppings, and bedding are all factors in the spread of the virus. It can also be transmitted mechanically - it is carried by people, other species of birds, and insects.

Clinical signs

Gumboro disease has a hyperacute course. The chicken dies within a week, sometimes even faster. Incubation period bursitis lasts from three to fourteen days.

Clinical manifestations are similar to coccidiosis:

diarrhea;
severe apathy;
trembling;
disheveled;
refusal of food;

A postmortem examination of a bird infected with the bursitis virus reveals characteristic signs indicating the cause of death - inflammation and hyperplasia of the bursa of Fabricius, heavy hemorrhages in the muscle tissue, skin and jade.
Such signs allow a clear diagnosis.

Important! Chickens killed by Gumboro disease die in characteristic pose- with outstretched paws and neck.

Pathogenesis

The disease is characterized by rapid spread: its pathogen, which enters the body orally, reaches the intestinal lymphoid cells within five hours. Rapid dissemination of the disease is achieved by the penetration of these cells into all circulating systems.

After 11 hours, the virus infects the bursa of the plant. Thus, after two days, infectious bursitis affects all organs. The main place of concentration of the virus is the bursa of Fabricius: it can remain there for up to two weeks.

Defeat lymphoid tissue leads to a pronounced immunosuppressive effect. The number of lymphocytes sharply decreases, and almost complete suppression of immunity is observed.
In general, immunity weakened by the Gumboro disease virus leads to increased morbidity in poultry viral hepatitis, salmonellosis, gangrenous dermatitis and coccidiosis.

Diagnostics

Clinical and pathological features make it possible to accurately diagnose the typical form of the disease. Identify an atypical course of the disease or establish it early stages allows laboratory research based on the isolation and identification of the virus.

To rule out bursitis when differential diagnosis, you need to make sure that the chickens are not sick:

lymphoid leukemia;
sulfonamide poisoning;
fat toxicosis.

Treatment

Due to the fact that the body of chickens that have recovered from the disease develops immunity to Gumboro disease, it was created large number live vaccines with a high degree of immunogenicity. The most common vaccines: Gumbo-Vax (Italy), LZD-228 (France), Nobilis (Holland).

Did you know?A chicken can be put into a state of hypnosis by gently pressing its head to the ground and drawing a straight line from the bird's beak with chalk.

Day-old chicks are vaccinated by drinking or intraocularly, young animals over three months of age are vaccinated intramuscularly. Antibodies from vaccinated individuals at high levels are transferred to chickens and protect them during the first month of life.

Prevention

To avoid the disease, you must:

provide the bird complete diet nutrition;
carry out cleaning and disinfection in a timely manner;
keep birds of different ages separately;
equip the poultry house with individuals of the same age;
incubate eggs separately own production and imported;
place day-old young stock brought from other farms separately from the main herd;
comply with the timing of preventive vaccination;
ensure the protection of the herd from the introduction of infection: purchase eggs and day-old young animals only from farms that are free from infectious bursitis;
strictly comply with zootechnical and veterinary requirements for keeping and feeding birds.

Compliance preventive measures and careful attention to the products purchased for incubation and young animals can significantly reduce the risk of infection of birds infectious bursitis. In the event that this does happen, the sick individuals must be destroyed.

gumboro disease(Disease Gamboro) (Infectious bursal disease - IBD, Infectious bursitis, infectious nephrosis) - disease of the bursa of Fabricius, highly contagious viral disease poultry of the chicken family, characterized by diarrhea, inflammation of the bursa of Fabricius, and immunosuppression. It is registered in a number of US states, in certain countries of Africa and Asia, in France, Italy, Germany and in other countries with developed poultry farming.

Pathogen information. The causative agent is an RNA-containing virus of the Birnae Viridae or Picornaviridae family, cultivated on embryos, causing their death on the 5-7th day. The pathogen can withstand heating up to 60°C for 1 hour, is resistant to ether, chloroform, and is sensitive to solutions of formaldehyde and caustic soda.

Epizootiological characteristics. Chickens of meat breeds aged 2-15 weeks are most susceptible to the disease. Infection occurs, as a rule, through the nutritional route.

Clinical signs and course. The incubation period is very short. The chickens show drowsiness, trembling, diarrhea, they eat little and drink a lot, their feathers are ruffled, and they die on the 4th day from the onset of the disease (3-80%). Unlike clinical form, the subclinical form is observed in chickens less than 4 weeks of age, when the immune system is damaged. Early manifestations of IBD are characterized by the absence of clinical signs and damage to the bursa of Fabricius, where the number of B-lymphocytes sharply decreases and immunosuppression develops.

The corpses are dehydrated. At autopsy, intramuscular hemorrhages are found in the chest and lower leg and other muscle groups. The kidneys are colorless, the liver and spleen are hypertrophied. The bursa of Fabricius is enlarged, edematous, and necrotic areas are noted on its mucosa. With a longer course of the disease, the volume of the bag decreases, and when it is opened, a curdled mass is discovered.

Diagnosis set on the basis clinical picture and the results of autopsy, laboratory tests (precipitation reaction in gelatin gel), which is based on the isolation of the virus, its identification, detection of antibodies in blood serum, and bioassay on susceptible chickens. Differentiate from infectious bronchitis, sulfonamide poisoning, mycotoxicosis, Newcastle disease, lymphoid leukemia, Marek's disease, fat toxicosis

Control measures. When a disease appears, the poultry house is isolated, and after slaughtering the birds, the premises are thoroughly cleaned and disinfected. For specific prevention, vaccination is used.

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Infectious bursal disease of chickens

Infectious bursal disease (IBD, Gumboro disease) is an acute contagious disease of chickens, characterized by damage to the bursa of Fabricius, diarrhea, nephrosis, and intramuscular hemorrhages.

The disease was first registered in 1957 in the town of Gumboro (USA), which gave the disease a second name.

Currently, the disease is registered in all countries of the world. Infection of herds ranges from 2 to 100% and is manifested by outbreaks of the disease. Economic damage consists of losses associated with the death of chickens, forced culling of poultry, a decrease in the meat productivity of young animals, as well as the costs of preventive measures And low level response to vaccination due to immunosuppression caused by bursa pathology.

Characteristics of the pathogen. The causative agent of IBD is a virus belonging to the family Birnaviridae (from the English bi - double, rna - ribonucleic acid), the genus Avibirnavirus. Virions of the virus are non-enveloped and are spherical particles with a diameter of 55 and 18-22 nm. They consist of a core containing double-stranded linear RNA and a protein - an icosahedral capsid, built of 92 capsomers.

Resistance to physical and chemical influences. The virus is resistant to ether, chloroform, changes in pH (2-11), and UV irradiation. When exposed to a 0.5% formalin solution, it is inactivated in 6 hours, 0.5% chloramine in 10 minutes.

Antigenic structure. Five proteins were found in the structures of virions. One of them is responsible for group specificity, the other for type specificity and the induction of virus-neutralizing antibodies.

Antigenic variability. The virus has antigenic variability: one serotype with six subtypes is pathogenic for chickens, two serotypes are pathogenic for turkeys. The presence of antigenic variability of the virus requires the use as a vaccine of a strain that has the maximum degree of antigenic homology with the epizootic strain.

Hemagglutinating properties. Not installed.

Virus cultivation. The IBD virus can be propagated in chicken embryos free of maternal antibodies to a number of viruses, including the IBD virus. When infected into the allantoic cavity or yolk sac, the embryos die on the 3-8th day after infection. Signs of virus replication in a chicken embryo are necrosis and hemorrhages on the body of the embryo, in the liver, and kidneys. The virus reproduces well in culture kidney cells and fibroblasts of chicken embryos, causing CPD on the 3-5th day after infection. It can be cultivated on SPF chickens (free from pathogenic flora) 21-25 days of age.

Clinical signs. In chickens 3-6 weeks of age, the disease is acute, but depending on the immune state of the livestock, a subacute course or death. The incubation period is 1-3 days, and the disease lasts 5-7 days.

Sick chickens exhibit diarrhea with the release of watery, whitish-yellowish droppings, then trembling of the head, neck, and deep prostration appear. Morbidity and mortality increase quickly and reach a maximum on the 3-4th day of illness, then within 5-7 days it usually declines. Distinctive features illness - suddenness, high level defeats and quick recovery. The mortality rate is 6-37%. Subclinical infection is expressed mainly by growth retardation. When an adult bird becomes ill, only a slight decrease in the percentage of embryo viability is observed.

Pathological changes. On different stages They are different diseases. Initially, hypertrophy of the bursa and petechiae in its mucosa, exudate with fibrin flakes between its folds, hemorrhages in the pectoral muscles and leg muscles, are noted. serous membranes. After a week, the lesions become different: serofibrous pericarditis, hepatitis and nephritis. A month after infection, the bursa atrophies and is 3-4 times smaller in size than in a healthy bird of the same age. Microscopic changes characteristic of IBD are found in the bursa of Fabricius of sick birds. They are mainly represented by necrosis of lymphoid and hyperplasia of reticuloendothelial cells, thickening of interfollicular connecting septa, and the formation of glandular structures instead of follicles.

Localization of the virus. The virus enters through digestive tract and affects lymphoid tissue. After 24-28 hours it is localized in the bursa of Fabricius. The most sensitive to the virus are lymphocytes, on the surface of which IgM is fixed. Therefore, the main target for the virus is the subclass of B lymphocytes, especially their immature forms. In addition, lymphocytes of the spleen, caecal glands of the cecum, etc. are destroyed. The immunosuppressive effect caused by the virus is explained by damage to lymphoid tissue.

CPD of immune complexes, including virus-infected lymphocytes, antibodies, complement, leads to the appearance of hemorrhagic lesions in skeletal muscles, liver and other organs. Precipitation of immune complexes in the glomeruli and convoluted tubules of the kidneys reduces their filtration capacity, and urate accumulates in the kidneys.

Diarrhea with IBD develops due to the reproduction of the virus in the intestinal epithelial cells, which leads to dehydration of the body. Weakening immune status poultry leads to additional infection with viruses and bacteria.

Source of infection- a sick bird. The pathogen is transmitted through infected feed, water, aerogenously, as well as through equipment and through eggs. Helminths and lice are considered direct vectors of transmission. Wild birds can be direct and indirect vectors. Under natural conditions, only chickens suffer from IBD, namely chickens 2-15 weeks of age. However, it was possible to isolate the virus from turkey poults, bats and mosquitoes.

Diagnostics. Only with a typical course is the disease relatively easily diagnosed based on clinical and pathological signs. In the early stages or in subclinical cases, laboratory tests are necessary.

Laboratory diagnostics. For laboratory studies, the bursa of Fabricius, liver, and kidneys are taken from birds that died or were killed during the first 7 days of illness.

Virus detection in pathological material it is possible to establish using express methods: indirect version of ELISA, RIF and PCR.

Virus isolation carried out by bioassay with subsequent isolation of the virus on chicken embryos, in cell culture and infection of chickens. It is not always possible to isolate the virus from affected organs, so a more reliable method for diagnosing IBD is serodiagnosis. Blood serum is also examined in asymptomatic cases of the disease. Important in the prevention of IBD has systematic monitoring of immune condition herds. Such control is carried out by examining paired blood sera.

Identification The isolated virus is carried out using PH on chicken embryos, in RIF and RDP.

Antibody detection to the IBD virus in the blood sera of sick and recovered birds is carried out in PH, RNGA, RDP, ELISA.

Virus-neutralizing antibodies reach maximum titers by the seventh day after infection and remain in the bird’s body for up to three months. Sera with a high titer of virus-neutralizing antibodies are usually positive in the RDP. RNGA detects antibodies already on the 3-5th day after infection with their maximum titers at 3-4 weeks. For wide serological study ELISA is used.

Differential diagnosis. IBD must be differentiated from infectious bronchitis of chickens, Newcastle disease, Marek's disease, Rous sarcoma, coccidiosis, nephritis, vitamin deficiency A. However, the detection of antibodies alone does not allow a diagnosis; it is necessary to isolate the virus, establish its serotype, subtype and virulence.

Immunity and specific prevention. When carrying out specific prevention measures, it is necessary to take into account factors that negatively affect the formation of stable immunity in poultry. This is primarily the type of antigen, the method and frequency of its use in the vaccination process, the degree of attenuation or inactivation.

When immunizing against IBD with a live vaccine, it is necessary to establish the compliance of the drug used with the epizootic strain circulating among birds. In addition, vaccination should be carried out taking into account maternal antibodies.

Currently, live vaccines from naturally weakened strains, as well as those weakened by passage on EC and in cell culture, are widely used. Birds have different age groups The intensity and duration of post-vaccination immunity are not the same. The level of specific antibodies in chickens corresponds to the concentration of virus-neutralizing antibodies in adult mother hens during the laying period.

Currently, dry live vaccines of the D-78 and Winterfield 2512 strains are used orally and in the form of a spray.

An inactivated vaccine is prepared from a virus propagated in EC and in cell cultures. The virus is inactivated with formalin or β-propiolactone, and aluminum hydroxide is added. The vaccine is used subcutaneously or intramuscularly, administered at the age of 2-4 months. Post-vaccination antibody titers are studied by ELISA and PH.

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Gumboro disease(Disease Gamboro), bursa of Fabricius disease, a viral disease of poultry of the gallinaceae family, characterized by diarrhea, inflammation of the bursa of Fabricius, and immunosuppression. It is registered in a number of US states, in certain countries of Africa and Asia, in France, Italy, Germany and in other countries with developed poultry farming.

The causative agent is a virus of the Reoviridae or Picornaviridae family, cultivated on embryos, causing their death on the 5th-7th day. The pathogen can withstand heating up to t 60°C for 1 hour, resistant to ether, chloroform, sensitive to solutions of formaldehyde, caustic soda. Chickens of meat breeds at the age of 2-15 weeks are most susceptible to the disease. Infection occurs, as a rule, through the nutritional route. The incubation period is very short. The chickens show drowsiness, trembling, diarrhea, they eat little and drink a lot, their feathers are ruffled, and they die on the 4th day from the onset of the disease (380%). The corpses are dehydrated. At autopsy, intramuscular hemorrhages are found in the chest and lower leg area. The kidneys are colorless, the liver and spleen are hypertrophied. The bursa of Fabricius is enlarged, edematous, and necrotic areas are noted on its mucosa. With a longer course of the disease, the volume of the bag decreases, and when it is opened, a curdled mass is discovered. The diagnosis is established on the basis of the clinical picture and autopsy results, laboratory tests (precipitation reaction in gelatin gel).

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Gumboro disease poses a serious threat to industrial poultry farming, causing high mortality and loss of productivity in both meat and egg chickens. The use of intermediate plus vaccines protects chickens from acute and subclinical forms of this disease. To study chicken blood sera for the presence of antibodies to the Gumboro disease virus, the ELISA method has been used for more than 15 years, which has a number of advantages, for example, it is fast and cheap, but its main advantage is that the method is reliable and standardized. This article presents the results of a study of broiler blood serum using ELISA during the growing period (from the 1st to the 45th day).

Protection throughout the growing period

One of the main objectives of vaccination against Gumboro disease is to protect chicks throughout the rearing period. Day-old chicks are protected from MA disease, which they received from chickens of the parent flock. Broiler chickens become sensitive to the Gumboro disease virus by 20 days of age, and egg-laying chickens by 30 days of age. The presence of MA in chickens early age prevents their vaccination, since MAs neutralize the vaccine virus (Fig. 1).

It has been proven that when immunizing chickens with a high level of MA, the vaccine virus does not cause seroconversion. When vaccinating chickens with a critical level of MA (the level of MA that the vaccine strain can overcome), a good immune response is formed that prevents clinical and subclinical signs of Gumboro disease - mortality, hemorrhagic inflammation of the bursa, and decreased productivity.
The chickens in early period(Fig. 2) the average antibody titer decreases, which reaches its critical value in chickens at 12 days of age (559). The chickens were vaccinated the next day. During a serological study, the first antibodies were detected on the 4th day after vaccination. The average antibody titer reached its maximum value at 26 days of age (3338) and remained at a high level until the slaughter of the bird (3398). The field virus can also cause seroconversion, but in this case, along with the latter, clinical signs appear and the productivity of chickens decreases. When assessing antibody titers (Fig. 3), it is also very important to take into account their homogeneity. High homogeneity indicates good quality vaccination of chickens.

Determining the date of vaccination

An equally important task of vaccinating chickens is to create a smooth transition from passive immunity (PA) to active immunity. However, in real conditions, calculate exact date Vaccination is only possible if the chicks come from the same supplier and from a homogeneous parent flock. Blood serum for serological testing is usually taken from chickens during the first three days of life.
Vaccination time is calculated using the Kohavena formula (for broiler chickens) or Deventor (calculation based on the decay period of antibodies).
These methods are often used in laboratories because they come with software equipment. The date of vaccination determined in this way must be confirmed veterinary specialist or manager, in accordance with real situation at the factory.
In this experiment, chickens were immunized with the Cevac® IBD L vaccine by feeding at 13 days of age (Ceva Santé Animal, Libourne, France). The average antibody titer in chickens before vaccination at 12 days of age was 559, with a larger number of samples (8) in the first group with antibody titers from 0 to 396 (Fig. 4). Coefficient of variation 97%. Chickens were immunized once with the intermediate plus vaccine Cevac® IBD L, since it overcomes the MA level at a dilution of 1:500.

Seroconversion and duration of antibody circulation

When studying blood serum samples from chickens at 26 days of age (2 weeks after vaccination), a high and uniform seroconversion was noted (Fig. 5), with a coefficient of variation of 32%. A positive antibody titer against Gumboro disease is considered to be from 1000 to 2000. In this study, the average antibody titer was 3338 and all samples were positive. The results of an ELISA study depend on many conditions - type of kit, operator skills, external conditions for setting up the reaction (temperature, humidity). It is possible to compare research results only if they were performed simultaneously, by the same operator and using kits from the same manufacturer.

The homogeneity of antibody titers can be assessed by the coefficient of variation (see Fig. 5). The diagram shows blood serum samples, which are distributed into groups: from 0 to 395, from 396 to 999, from 1000 to 1999, etc. It is conventionally accepted that for statistical reliable results when performing ELISA, it is necessary to select from 18 to 23 (18 minimum) blood serum samples. Information in the form of a diagram allows you to evaluate the arrangement of titers by group (most samples in one group or samples distributed in several groups) and in relation to the average value (heterogeneous or homogeneous titers). When studying the blood sera of day-old chicks (see Fig. 3), most antibody titers were located in one group and were close to the average value.

Good homogeneity and high level of MA indicate satisfactory condition the health of the parent stock and the correct vaccination program for chickens before laying using live and inactivated vaccines.

Many studies have noted a positive correlation between the virus neutralization reaction and the ELISA method. In addition, differences in mean titers between two groups of chickens vaccinated with different vaccines do not always indicate the immunogenicity of the vaccine. For example, the average antibody titer of 3000 in 25-day-old chickens immunized with vaccine A and 4500 in chickens vaccinated with vaccine B does not mean that immunization is better when using vaccine B. We can only say that chickens of both groups were successfully immunized. Differences in mean titer may be due to differences in kits or other conditions. The average titer value can be used to assess the quality of vaccination (bad or good), but not to compare different vaccines. With ELISA, the most significant criterion for assessing the results is the homogeneity of titers, which depends mainly on the quality of the vaccine, the conditions of its transportation and storage, and the technique of vaccinating chickens. To check the quality of vaccination, you can carry out additional research blood serum samples from 45-day-old chickens. In these studies, the average antibody titer in 45-day-old chickens was 3398 (Fig. 6) with a coefficient of variation of 23% (high homogeneity).