Cattle are prone to respiratory disease because of the design of their lungs and airways. Because anatomy can’t be altered, herds must be managed to reduce the incidence of lung disease.
Cattle have a poor lung design. Their air passages (trachea and bronchi) are fairly large, yet their functional lung tissue where oxygen uptake occurs is fairly small.
Because a cow has relatively little lung volume compared to airway volume, it must breathe harder and faster than many other animals to get the same amount of oxygen into its bloodstream.
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A cow could never be a performance animal like a horse that needs to take in a lot of oxygen rapidly during periods of exertion.
The design of cattle lungs also predisposes them to collapse. Alveoli are the tiny sacs that make up the functional lung tissue where oxygen transfer occurs.
In most species, alveoli are connected with tiny tunnels. When fluid or pus builds up in one alveoli, the pressure in others will help force it out. Cattle have few connecting tunnels so alveoli can’t easily drain.
Once they collapse, surrounding alveoli are unable to help inflate them. Calves can have an entire lung lobe collapse and not be able to inspire enough air to inflate the thousands of microscopic alveoli.
Cattle are also predisposed to respiratory disease because of the design of the filtering mechanisms in their noses and airways. Air that enters the nose must turn many corners among the mucous-covered nasal lining.
Since particles in inhaled air tend to move in straight lines, they run into the mucous and get trapped. If cows are stressed and have to breathe heavily, the filtering process is not effective because the air is passing so rapidly that particles are able to stay suspended in the air.
Microscopic hairs called cilia are also part of the filtering system. They move mucous out of the nasal passages and also up the trachea to be swallowed.
Extremely cold weather, dust, viral diseases and engine exhaust fumes can reduce the amount of mucous produced and impair the movement of these cilia. Under these conditions, dust and disease organisms can readily penetrate deep into the lungs.
Any particles that get past the filtering mucous and cilia can end up in alveoli. At this deep level of the lung, there are cells that destroy and neutralize disease pathogens.
These cells work their way up the respiratory tract to where mucous and cilia can carry them out.
This cellular defence mechanism can be adversely affected by glucocorticoids that are released as a result of stress. Cell activity is also impaired by poor nutrition, cold stress, or something as simple as an acidosis due to grain overload.
Producers can help protect their cattle from infectious respiratory disease by stimulating immunity in the nasal passages.
Intranasal vaccines are good at causing the secretion of antibodies into the nasal mucous. These antibodies will neutralize infectious agents as they are inhaled.
When all defence mechanisms fail, the lungs are open to infection. Minimizing stress, preventing infectious disease by vaccination and providing clean air are important steps toward reducing respiratory disease.
