EQUINE BRONCHOALVEOLAR LAVAGE CYTOLOGY - SURVEY OF THOROUGHBRED RACEHORSES IN-TRAINING

Sixty-two Thoroughbred horses aged between 1 and 7 years in training i n Sydney had bronchoalveolar lavage (BAL) samples collected for cytolo gical examination. All horses, except the yearlings and those with a c ough, had raced at the time of the examination and the trainers report ed satisfactory performance. Free erythrocytes were found in 73% of sa mples and haemosiderophages In 90% of the samples, indicating immediat e or past occurrences of exercise-induced pulmonary haemorrhage (EIPH) . Bronchoalveolar fluid from the yearlings contained significantly les s (P < 0.05) erythrocytes and haemosiderophages than samples from hors es in other age groups. In the older horses, there was also more haemo siderin within the macrophages. No differences in BAL cytology could b e attributed to gender, and there was no relationship between BAL cyto logy and racing performance. The main cytological findings were (mean +/- sd): total nucleated cells - 832 +/- 578/muL with the main cell ty pes being: macrophages - 59 +/- 10% (haemosiderophages - 20 +/- 24%); neutrophils - 9 +/- 6%; lymphocytes - 31 +/- 9%. The erythrocyte count was 10.3 +/- 17.7% of the total cell count. Horses with chronic cough ing had a higher proportion of macrophages and a lower proportion of l ymphocytes in the leucocytes obtained from BAL. There was a higher occ urrence of EIPH detected in BAL findings than that previously reported when endoscopic examination has been used to diagnose EIPH. The occur rence and severity of EIPH as indicated by the BAL findings was found to be related to exercise intensity. The cytological findings were sim ilar to those reported in horses in the northern hemisphere. We conclu de that BAL cytology may be useful in the diagnosis of various lower r espiratory tract disorders and that exercise-induced pulmonary haemorr hage occurs in virtually all horses in race training.