In the grass-roots farms or veterinary clinics, whenever this happens, everyone either thinks that the medicine is not good or feels that the disease is difficult to treat. Few people do a comprehensive analysis, then find the root of the problem and solve it? For example, at the beginning of this year, in Dalian, Northeast China, both laying hens and broiler breeders were found to have a high incidence of atypical bursal disease, and many people didn't care, resulting in unsatisfactory medication effect.
Bursa of fabricius: immune organ of chicken
Bursa of fabricius is an important immune organ in chickens. If bursa of fabricius is destroyed, bacteria, viruses and protozoa will easily enter the body and other diseases will break out, and the source is bursal disease. Therefore, after the outbreak of bursal disease, many chickens will be difficult to raise and manage.
Then, in addition to bursa of fabricius, the immune organs of chickens include Hartmann's gland, thymus, cecal tonsil, etc. There are always four main immune organs in chickens. If some viral diseases occur in chickens, it will invade the thymus and cecal tonsils, and Hartmann's gland will also be disturbed and affected, and then a series of diseases will be infected.
Therefore, it can be seen that, such as Hartmann's gland, bursa of fabricius, thymus, cecal tonsil, etc., are all very important immune organs in chickens.
What are the primary immune organs?
The thymus of the chicken is located under the skin on both sides of the neck. There are 7 leaves on each side of the chicken and 5 leaves on each side of the duck. Each leaf is like a lentil, and it is chain-shaped and red or yellowish. After the sexual maturity of poultry, the thymus will degenerate, leaving only traces.
Multifunctional stem cells from bone marrow differentiate and mature into T lymphocytes in thymus. Most of them are also transferred to the spleen and other secondary immune organs for storage. When an antigen enters the body, generally speaking, T cells and B cells make an immune response at the same time. The B cell response product is a specific antibody, and the T cell response product is an effector cell. The two complement each other and jointly destroy the antigen.
The bursa of fabricius is a unique immune organ of birds, which is located above the cloaca. Chicken's bursa is pear-shaped and duck's bursa is cylindrical. There are many folds on the inner wall of the capsule, and there is a very thin short tube at the bottom of the capsule cavity that communicates with the cloaca. The bursa of fabricius of chicken is about the size of pea at 3 weeks old, and it is the largest at 4 weeks old, which is about the size of grape. Duck's bursa of fabricius is the largest at the age of 3 months, about as thick as a pencil and 2 cm long. After sexual maturity of poultry, bursa of fabricius gradually degenerates.
What are the secondary lymphoid organs?
Secondary lymphoid organs include: bone marrow, spleen, Hadrian's gland, conjunctival associated lymphoid tissue, bronchial associated lymphoid tissue and intestinal associated lymphoid tissue.
Bone marrow is a hematopoietic organ and an important immune organ. Bone marrow can produce a special kind of cells, called "multifunctional stem cells", which will differentiate into different immune cells when they travel to different parts of the body with blood, such as B lymphocytes when they travel to bursa of fabricius, and T lymphocytes when they travel to thymus, and all immune cells in the body are differentiated from it. In addition, bone marrow itself is also the place where pluripotent stem cells differentiate into some immune cells.
The spleen is located at the upper right of the glandular stomach. The spleen of adult poultry is about the size of ginkgo and is brownish red. The spleen of chicken is nearly spherical, and that of duck is slightly triangular. There are B cells from bursa of fabricius and T cells from thymus in spleen, which is an important place for immune response and the production of antibodies and effector cells.
Only the cecal tonsil is obviously visible to the naked eye. In addition, there are diffuse lymphoid tissues in the mucosa of many organs, and the Hadrian's gland lymphoid tissues in the eyes are the most abundant.
Immune system: an important defense barrier
The immune system of poultry refers to a complete anatomical system consisting of organs, tissues, cells (lymphocytes, etc.) and molecules (antibodies) with immune function in chickens and a structure with certain physiological functions. The immune system mainly includes central immune organs, peripheral immune organs and various immune cells involved in immune response.
The structure and function of immune organs of chickens and other birds are basically similar to those of mammals, but there are some differences, the most important of which is that birds have a special immune organ-bursa of fabricius. In addition, chickens and most birds have no lymph nodes, but only aggregated lymphoid tissue.
Immune organs are divided into central immune organs and peripheral immune organs. The central immune organ of chicken is composed of thymus and bursa of fabricius, which plays a dominant and decisive role in the development of peripheral lymphatic organs. In addition, Hadrian's gland is a collection of lymphoid tissues beside the eyes, and a large number of plasma cells are infiltrated between epithelial cells in the supraorbital gland located right behind the eyes, which is mainly responsible for the local immunity of the eyes, nose and upper respiratory tract. Therefore, chickens can obtain secretory antibodies by dropping vaccines on their eyes and nose during immunization, which plays a role in local immunity.
Chicken spleen is small and round, located on the right side of the stomach. There is a connective tissue capsule on its surface, including spleen marrow which is soft and brittle inside, and contains reticular cells, B cells, macrophages, plasma cells and various blood cells. Therefore, immune cells in the spleen have strong phagocytosis and filtration effects.
What harm can immunosuppression cause?
At present, the problem of poultry immunosuppression faced by poultry breeding industry actually occurs in all parts of the country. It is only because of the development of vaccine technology and frequent immunization, as well as the extensive and frequent use of various health care products, that the virulence of viruses such as throat transmission, transmission, influenza and bursa of fabricius is greatly reduced. Some of them have developed from strong transmission and caused typical clinical symptoms and death to low virulence and turned to low pathogenicity and recessive asymptomatic infection.
In clinical diagnosis, sometimes chickens don't die, so it is normal for farmers and veterinarians to ignore them. However, not showing symptoms in clinic does not mean that they are harmless to chickens. Especially when other diseases occur in chickens, the harm is actually very great. For example, the respiratory diseases that occurred frequently in the Central Plains last month were difficult to treat, which was caused by the existence of recessive or subclinical laryngeal transmission.
These immunosuppressive diseases are mainly manifested in the clinical occurrence of chicken diseases such as respiratory diseases, colibacillosis, salpingitis and peritonitis, which are treated with various drugs and prescriptions, but the effect is not good or easy to repeat. This is mainly due to the existence of immunosuppression, which makes the body always unable to "establish an effective defense barrier" under the stimulation of antigens. Careful diagnosis will reveal that the thymus gland is smaller than normal, or there is mucus in the bursa of fabricius, or the spleen is fragile and easy to rupture, which deserves vigilance and attention in diagnosis and treatment.
Treatment: Enhance immunity and resist virus.
1. Enhancing immunity is not medication, but strengthening feeding management with biological safety as the core, such as disinfection to remove the source of infection if necessary. If fewer viruses enter the body through the respiratory tract and digestive tract, the immune power of the body against foreign invaders will be less, and its immunosuppression will be greatly improved.
2. Strengthen the purification of various pathogens of breeder chickens and cut off vertically transmitted diseases; According to the analysis of the influencing factors of feed formula, feed nutrition is optimized to increase the immunity of animals from the perspective of dietary nutrition balance. Amino acids, vitamins, biotin, etc. all have the effect of improving the body's immunity from the nutritional point of view, which is much more economical and cost-effective than medication.
3. During the treatment, in addition to the corresponding drugs for etiological treatment, the drugs for enhancing immunity and anti-virus such as inosine, interferon, polycyocyte, transfer factor, interleukin, astragalus polysaccharide and thymosin should be combined to enhance the therapeutic effect of the drugs for etiological treatment and eradicate the cause.
4. Use some "antiviral" or "immunity-enhancing" Chinese veterinary drugs with Astragalus, Ginseng, Codonopsis pilosula as the main components.