Pasture-associated severe equine asthma (EPA) is a progressive condition affecting horses in the southeastern United States. Pulmonary function testing with methacholine challenge (MC) provides a definitive diagnosis by eliciting airway hyper-responsiveness. Most horses require extensive conditioning to accept the instrumentation. Our hypothesis was that MC protocols designed to elicit airway hyper-responsiveness would yield equivalent results in the presence and absence of sedation. Sedated and unsedated MCs were performed on 8 EPA-affected horses, with each horse acting as its own control. Acepromazine was superior to xylazine/butorphanol, resulting in sedation and data collection. Based on American Thoracic Society guidelines, an acceptable ability to detect differences in lung resistance is less than a twofold difference in the provocative concentration of methacholine that elicited a 40% increase in lung resistance (PC40RL). Significant differences in PC40RL were not detected. Validation of a sedation protocol for use in MC will expand the application of this diagnostic.

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