RESPIRATORY TRACT INFECTIONS IN CATTLE

In the article a literature review of Bovine respiratory diseases (BRD) is presented. Respiratory diseases are considered to be one of the most harmful diseases of cattle, which cause great economic damage for the operators of the cattle industry. The BRD complex is a multifactorial and multi-etiological disease. The BRD complex is a multifactorial and multi-etiological disease. The main factors providing the BRD development are the management status of rearing cattle, the impact of the environment and pathogens. Without neglecting the importance of the first two factors, pathogenic microorganisms remain the major etiological factor of BRD. Respiratory tract infections in cattle are caused by viruses and bacteria, moreover the diseases often develop in an associated form. However, the bacterial factor in the etiology of respiratory diseases plays a main role. Mannheimia haemolytica serotype 1 is the main pathogen of BRD, which can cause disease as a single etiologic agent and as in association with other pathogens (Histophilus somni, Mycoplasma bovis). In most cases, fibrinous pneumonia or fatal acute pneumonia is often associated with Mannheimia haemolytica. Pasteurella multocida is considered to be a less virulent bacteria than Mannheimia haemolytica, and for a higher level of infection need to initiate the inflammatory process in the respiratory tract of animals. Pathogenic strains of Pasteurella multocida serogroup A are a significant etiologic factor of severe enzootic pneumonia in dairy calves. Respiratory diseases caused by mycoplasma remain one of the serious infectious diseases of cattle. Mycoplasma bovis is the most invasive and dangerous mycoplasma for young cattle. This type of mycoplasma is usually present in the upper respiratory tract of clinically healthy calves who are bacterial carriers. When the zootechnical conditions of brieding and feeding the calves are disturbed and for other stress factors there is an active proliferation of mycoplasmas and they successfully colonize the lower respiratory tract of the animals, causing an inflammatory process in the lungs. Other commensal bacteria of the upper respiratory tract, Histophilus somni, can cause pneumonia that usually occurs in subacute or chronic form. The pathogenic forms of this bacteria are often isolated together with Mannheimia hemolytica. Other opportunistic bacteria (Arcanobacterium pyogenes, Streptococcus pneumoniae, Staphylococcus aureus, Chlamydiales spp., Fusobacterium necrophorum, Corynebacterium bovis) may be etiological factors for the development of BRD. Depending on the etiologic agent, the clinical symptoms of calf bronchopneumonia have some specificity, herewith the degree of lung damage depends on the duration of the disease and the virulence of the pathogen.