Comparative cytology of bronchoalveolar lavage fluid from asymptomatic horses after being moved from pasture to a stabled management regimen

Introduction: Stabling has been identified as a risk factor for equine asthma. The objective of this study was to analyze bronchoalveolar lavage (BAL) cytology in horses without signs of lower respiratory disease, before and after being subjected to a 30-day stabled regimen at the Hospital Escuela, Facultad de Ciencias Veterinarias, UNLP.

Materials And Methods: 5 male equines, age range 7-17 years, of different breeds were used. The regimen consisted of daytime paddock turnout and night stabling in boxes with wood shavings bedding. They were fed alfalfa hay and grains. Two samples were taken, the first BAL was performed 24 hours after admission (they had been at pasture for 90 days), and the second BAL was repeated a month later. Cytology reference values were based on the latest consensus on inflammatory airway disease of the American College of Veterinary Internal Medicine.

Results: In the first BAL, 4 animals presented a slight increase in the number of neutrophils and/or mast cells. One horse was diagnosed as subclinical asthmatic due to presenting more than 5% of mast cells and maintained high levels after 30 days. Although all of the animals remained asymptomatic, there was a variable increase in the proportion of active macrophages, neutrophils and mast cells. Eosinophils were absent in the first sample and then present in all horses (above the reference value in 3 horses). After the second BAL, two other cases of mild subclinical asthma were diagnosed, one due to an increase in eosinophils and the other in mast cells.

Discussion/Conclusions: This study demonstrated that BAL is an effective method for the early detection of pulmonary inflammation and allowed to associate housing with an increase in macrophage activity and mild inflammation, showing the heterogeneity in the inflammatory response of the lower airways in horses with identical exposure.

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