Objective - evaluate horses with acute airway obstruction using three treatment regimens: tapering doses of dexamethasone (DEX), environmental modification (ENV), and a combination of both treatments (DEX + ENV) by analyzing clinical parameters, pulmonary function testing, bronchoalveolar lavage fluid (BALF) cytology and BALF cell expression of the cytokines IFN-? and IL-4 Animals - 6 horses with recurrent airway obstruction (RAO) Procedures - Clinical examination, pulmonary function test, and collection of BALF prior to treatment and during 22 day treatment period Hypothesis - Alterations in clinical parameters, pulmonary function and airway inflammation in acute equine RAO will return to remission values by treating with DEX, ENV or DEX + ENV Results - All horses demonstrated clinical disease, reduced pulmonary dynamic compliance (Cdyn) and an increased maximum change in pleural pressures (?Pplmax) when in a challenge environment. All treatments improved clinical parameters, ?Pplmax and Cdyn. BALF cytology during an RAO crisis demonstrated neutrophilic inflammation. ENV or DEX + ENV resulted in a significant decrease in airway neutrophilia that was maintained throughout the treatment period. In contrast, treatment with DEX caused a reduction in airway neutrophilia initially followed by a rebound neutrophilia as the period between administrations of dexamethasone (0.05mg/kg) was increased to 72 hours. The rebound neutrophilia was not accompanied by equivalent deterioration in clinical parameters or pulmonary function. Conclusions - Environmental modification is important in the management of RAO horses. Treatment of clinical RAO with a decreasing dosage protocol of corticosteroids in the absence of environmental modification results in the persistence of airway inflammation without recrudescence of clinical disease. / Master of Science

Background – Feeding horses round bale hay (RBH) has been associated with airway inflammation. The purpose of this study was to determine if horses fed RBH for a 6-week period demonstrated more evidence of airway inflammation than horses fed square bale hay (SBH) of comparable quality. Hypothesis - The respiratory health of horses fed RBH will not differ from horses fed SBH of comparable quality. Animals – Two feeding groups of 15 healthy horses (mixed ages, breeds) from the University riding program. Methods – This was a prospective study performed during fall of 2009. At the beginning and end of a 6- week feeding trial, horses were examined (physical, upper airway endoscopic) and samples (tracheal aspirate (TA), bronchoalveolar lavage (BAL)) collected for cytology and/or bacterial/fungal culture. Hay was analyzed for nutritional value and bacterial/fungal content. Results – Horses fed RBH demonstrated an increase in pharyngeal lymphoid hyperplasia (p=0.0143) and percentage neutrophils (p=0.0078) in the TA samples post-feeding as compared to pre-feeding values. Nutritional analysis of hay and measurements of bacterial/fungal load did not differ over time and/or between hay types. Conclusions and clinical importance – The identification of airway inflammation in the horses fed RBH indicates that factors associated with the manner in which the hay is fed and consumed contribute to the development of subclinical airway inflammation. RBH affords horses continuous daily exposure to hay and as horses bury their muzzles in the bale, exposure to particulate matter is likely increased. These factors may partially explain the response in horses fed RBH. Further studies are required to confirm these predictions. / Master of Science