The bovine respiratory disease (BRD) has increased drastically since the ’70s -’80s and is now endemic in intensive farming, especially in meat farms.
This is mainly due to the cattle delicate and relatively small lung volume which under stress conditions (transport, early weaning, manipulation, environmental variations) and in a crowded environment rich in pathogens as intensive farming is, is easily attacked due to decreased cell-mediated immunity.
How can we limit the damage and what are the factors that favour this disease?
Temperature and humidity:
High ambient temperature associated with low humidity increase mucus viscosity, decreasing the mucociliary activity in the respiratory tree.
Abrupt cooling leads not only to a decrease in cellular capacity to remove foreign materials (phagocytosis), but also to vasoconstriction and to alterations of the pulmonary surfactant (a complex of lipids and proteins essential for respiration as it prevents the collapse of the smaller alveoli and the excessive expansion of the largest).
High values of carbon dioxide (CO2), ammonia (NH3), and hydrogen sulphide (H2S) reduce mucociliary activity, the first barrier that protects cattle from pathogens. In particular, ammonia has a toxic action on the body mucous membranes, which leads to the fall of vibratile cilia and the rupture of alveoli, thus rendering the bovine vulnerable to bacteria and viruses present in the stable.
The “smell test” (that is when we perceive smell of ammonia) comes too late: at a concentration of 10ppm the first problems arise and at 20ppm the lungs’ activity of the cattle is compromised.