ISSUE FOCUS 64 FEED & ADDITIVE MAGAZINE September 2024 foreign particles away, while mucus secreted by goblet cells keeps epithelial moisture and traps particles and pathogens (Figure 1). Any outside influence that lowers the immune system’s activity or impairs the respiratory cilia’s function is a risk factor for respiratory disease. Depending on the production region, climate plays a key role in the occurrence of respiratory disease. Cold and wet weather, fog levels with little air exchange and low UV radiation favour the spread of infections. Strong temperature fluctuations between day and night also put a strain on the animals' immune system. In hot climates, high temperatures and humidity make it easier for microorganisms, secondary particles, and toxic metabolites to attach to the particulate matter entering the respiratory system . Elevated levels of dust or fungal spores irritate the animals' respiratory tract, causing localised inflammation and paving the way for other pathogens such as virus and bacteria. Bacterial infections often require antibiotics, driving the spread of antibiotic resistance. Young animals are especially at risk. A still weak respiratory system, an underdeveloped immune system and weaning stress are often the causes of respiratory disease. Respiratory problems in young animals can lead to lung damage which can impair the animal's performance and consequently reduce financial returns throughout the entire production process. Lung lesions are a common occurrence at slaughterhouses in cattle as well as pigs and research has shown a clear connection between damaged lungs and performance reduction and money loss. In swine production, productivity loss can reach up to 14 US-Dollar per pig, while bovine respiratory disease syndrome can lower the net revenue per animal by 35% or more in feedlot operations due to veterinary treatment costs and negative implications for health and performance. Figure 1. Barrier function of the ciliated airways: Mucus production b), liquefication of the mucus c), and removal of dust and pathogens from the airways d)
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