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

Sixty-two Thoroughbred horses aged between 1 and 7 years in training in Sydney had bronchoalveolar lavage (BAL) samples collected for cytological examination. All horses, except the yearlings and those with a cough, had raced at the time of the examination and the trainers reported satisfactory performance. Free erythrocytes were found in 73% of samples and haemosiderophages In 90% of the samples, indicating immediate or past occurrences of exercise-induced pulmonary haemorrhage (EIPH). Bronchoalveolar fluid from the yearlings contained significantly less (P < 0.05) erythrocytes and haemosiderophages than samples from horses in other age groups. In the older horses, there was also more haemosiderin within the macrophages. No differences in BAL cytology could be attributed to gender, and there was no relationship between BAL cytology and racing performance. The main cytological findings were (mean +/- sd): total nucleated cells - 832 +/- 578/muL with the main cell types 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 coughing had a higher proportion of macrophages and a lower proportion of lymphocytes in the leucocytes obtained from BAL. There was a higher occurrence of EIPH detected in BAL findings than that previously reported when endoscopic examination has been used to diagnose EIPH. The occurrence and severity of EIPH as indicated by the BAL findings was found to be related to exercise intensity. The cytological findings were similar to those reported in horses in the northern hemisphere. We conclude that BAL cytology may be useful in the diagnosis of various lower respiratory tract disorders and that exercise-induced pulmonary haemorrhage occurs in virtually all horses in race training.