Pneumonia in calves has a complex etiology with many pathogens implicated in this syndrome. Pnuemonia may be caused by viruses, bacteria, mycoplasmas and usually a combination of them.
Causes of pneumonia in newborn calves:
- coli and salmonella infections (pnuemoenteritis).
- Fusobacterium necrophorum.
- Klebsiella pneumonae.
- Mannhemimia (Pasteurella) haemolytica.
- Pasteurella multocida.
- Histophilus (haemophilus somni).
- Several viruses “parainfluenza-3, adenovirus, rhinovirus, reovirus, BVD, IBR”.
A complex of biochemical, physiological and immunological defense mechanism protects the respiratory tract of the calf against the inhaled particles. This includes the aerodynamic filtration by the nasal cavities, sneezing, cough reflex, mucociliary transport mechanism, local and systemic antibody systems and alveolar macrophages.
Respiratory mucociliary clearance mechanism plays an important role in protection of the respiratory tract against infection. Mucous traps and transports inhaled particles to pharynx where they are swallowed; also it keeps the underlying mucosa hydrated. Mucous contains antibodies especially IgA which together with lactoferrin and lysozyme provide immunological defense. In case of infection the mucociliary clearance is impaired due to disruption of effective ciliary activity and changes in quantity or quality of the mucous.
In viral infections, ciliary activity is disrupted due to deciliation or lesions of the respiratory mucosa.
Stress is one of the most important factors which play a role in buildup of respiratory infection. Stress, generally reduces the resistance to infection due to the high adrenocortical activity. Exposure of calves to adverse environmental conditions, transportation, and weaning increases their susceptibility to respiratory infection.