Results
Descriptive analyses
During the data collection period, a total of 737 samples were received
at the diagnostic laboratory. Data control was performed and duplicates
were removed, as only the first sample from a horse was included.
Finally, six hundred and four BAL samples were included, originating
from 70 different veterinary practices around Denmark. Forty-seven
different horse breeds were represented, with warmblood (n=108) and
Icelandic horse (n=89) being the two most common breeds. The mean age of
the total population was 10.5 (±4.5) years (Table 1). Bronchoalveolar
lavage differential cell counts were done for all horse samples included
(Table 2).
Clinical signs
An anamnesis of poor performance without concomitant coughing was not
associated with TMS (p=0.060). Horses without an anamnesis of coughing
and poor performance, and horses with only poor performance had
significantly lower levels of BAL neutrophils compared to the group of
horses with coughing (p=0.009 and p=0.001, respectively) and the group
of horses with both poor performance and coughing (p=0.005 and
p<0.001, respectively). No differences were found between
horses with clinical signs coughing or poor performance and the
percentage of BAL mast cells (p=0.129).
Tracheal mucus score
A TMS was available for 448 horses, and a significant association
between TMS and asthma types was found (p<0.001). The largest
contributions to the differences between the observed and expected
values in the Chi-square test were due to horses with normal BAL
cytology having a TMS of 1 (14.8%), while horses with SEA had a higher
frequency of TMS score 4 (15.7%) and score 5 (14%). The TMS plotted
against the different BAL cytology diagnosis in shown in figure 1.
The further specification of horses diagnosed with MEA and
differentiated into MEA neutrophilic, MEA mastocytic, or MEA mixed
diagnoses revealed significant differences in TMS (p<0.001)
(Table 2). Horses with normal BAL cytology had a higher frequency of
lower TMS scores compared to horse with SEA, with a contribution of
horses with normal BAL cytology /TMS scores 0-1 of 13.8% vs. SEA/TMS
score 4-5 of 26.7%. Amongst the differentiated asthma types, the MEA
mastocytic accounted for the highest proportion of differences in TMS
scores with a total contribution of 9%, followed by MEA neutrophilic
6%, MEA eosinophilic 3% and MEA mixed 1.6%. No significant
association between TMS and BAL mast cell count was found.
BAL volume aspirated
The BAL volume aspirated was available for 540 horses. No significant
difference was found for the group of horses with normal BAL cytology
values compared with the group of horses with MEA (p=0.076), but
significantly higher compared to the group of horses with SEA (50.0%
vs. 40.0%, p=0.035) (table 2).
No significant difference between the BAL volume aspirated and the age
of the horse was found, neither when horses were sub-divided into age
groups (p=0.139).
Housing
Information on housing (single box or loose-housed in groups) was
collected for 523 horses. The Chi- square test revealed dependency
between housing and EA groups (p=0.011). Of the horses in loose-housed
groups 28% had normal BAL cytology, 34% had MEA and 38% had SEA. Of
the horses housed in single boxes, 19% had normal BAL cytology, 49%
had MEA and 32% had SEA diagnosis (Figure 2). Information on roughage
fed (divided into dry hay n=186, soaked hay n =56 or haylage n=254) was
available for 496 horses, the Chi-square test revealed dependency
between roughage fed and EA groups (p<0.001). Of the horses
with the SEA diagnosis, 56% were fed hay, 14% were fed soaked hay and
30% were fed haylage at the point of examination. For the horses with
the MEA diagnosis, 27% were fed hay, 10% were fed soaked hay and 63%
were fed haylage.