Recurrent
airway obstruction (RAO) or “heaves”, the equine equivalent of
human asthma, is a common cause of poor performance and a significant
welfare concern.
Severely affected
animals show signs such as dilated nostrils, nasal discharge, and
excessive chest movement. A "heave" line may be present.
They may be incapable of any athletic activity. Mild cases may appear
to breathe normally and require further investigation to confirm the
diagnosis. However, most cases fall somewhere between the two
extremes.
The
signs are caused by a combination of increased mucus production in
the respiratory tract and spasm of the muscles surrounding the
airways. This results in narrowing of the airways, making it more
difficult for the horse to breathe.
Recent
research, funded by the Horserace Betting Levy Board, has been
looking at the properties of mucus and the sites of its production in
the lungs of horses with RAO.
An
essential component of mucus is the mucins – high molecular weight
proteins, produced by specialised cells such as those lining the
respiratory tract. Their most important characteristic is that they
can form gels, and so provide lubrication, transport and a physical
barrier.
It
was these mucins that formed the subject of this study. A summary of
the work, carried out by Adele Williams as part of her PhD studies at
the University of Manchester, has been published online.
Dr
Williams found no difference in composition of the mucus between
healthy and RAO-affected horses; the RAO cases just had more of it.
Neither did she find any difference in mucin properties between
horses housed inside or maintained at pasture.
The
research showed that mucins were produced in cells lining the airways
and in deeper glands. There was great variation in the size and
number of these cells in both normal and RAO-affected horses.
However, the mucin-producing cells in the deeper glands were larger
in horses with RAO than in healthy control animals.
In
the future it may be possible to use cell cultures to study mucus
production in the laboratory, and to investigate ways of modifying
mucus production. As part of the current project, mucin-producing
cells were grown successfully in the laboratory for a short time.
However there were problems with bacterial and fungal overgrowth. The
technique needs to be refined before it can be used for analysing and
modifying mucus production in the search for a treatment for mucus
overproduction in horses with recurrent airway obstruction.
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