A natural filter

THE respiratory system prevents harmful substances entering a horse’s lungs…

1 Hairs inside the nostrils obstruct larger particles.

2 Humidification in the nasal sinuses and pharynx moistens particles, making them heavier and stickier.

3 The conchal sinuses generate a swirling airflow that drives medium-sized particles into the mucuscovered sinus linings.

4 In the pharynx, which acts as a holding chamber where air pauses between each breath, particles sink or spread to the sides and become trapped by mucus.

5 The trachea (windpipe) speeds up airflow. This sweeps remaining particles on to its mucus-covered sides, where multiple cilia

(tiny hairs) transport them back up to the pharynx to be swallowed or snorted away.

If a horse is placed in an environment that overwhelms this natural filtering, airway inflammation and mucus accumulation can result.