Respiratory Disease - Winter Coughs and Colds

Like humans, horses often catch a ‘cold’ during the winter months as viruses
in particular are more easily spread and the animal’s immune system may be
compromised by the stress of cold weather.
The respiratory system is paramount to a horse’s ability to exercise and
perform. This vital system is hidden in the depths of the thoracic cavity
(chest), taking up almost 50% of a horse’s body ‘barrel’ capacity. However, in
many cases, only very subtle signs, such as a slight ‘wheeze’ or cough, are the
only outward signs which indicate that potentially debilitating airway disease is
affecting your horse.
The lower respiratory tract within the lungs is subjected to heavy insult during
exercise from a variety of inhaled bacterial and viral micro-organisms, as well
as allergens, including moulds and dust, which can increase airway reaction and
excess mucus production as a form of bronchitis. Pollutants, such as ammonia,
an irritating gas released from the stable bedding, as well as inhaled cold air
during early morning training without adequate pre-exercise warm up, especially
in winter, increase the risk of compromising the defences and efficiency of the
respiratory system.
Most of the inhaled microbial and irritant particles lead to airway allergy, low
grade infection, increased mucus build-up often with partial airway shutdown
due to broncho-constriction. Once the lower airways in the lungs are affected,
the slow response of the immune system external to the blood and body
tissues, increases the risk of chronic lower airway disease, combined with
continued airway insult during exercise.
There are a number of infective organisms which can result in
inflammation and low grade infection within the respiratory tract.
In Australia, the Equine Herpes Virus (EHV-1, EHV-4 subtypes)
commonly referred to as the ‘stable virus’ is the most widespread viral
disease which results in ‘flu’ like symptoms in horses of all ages. Studies
indicate that up to 40% of long term airway disease, especially in young horses
in training, is caused by ‘stable virus’ infection. Often young horses, especially
weanlings under the physical and mental stress of weaning, cold weather and
grouped with other young horses, have a high incidence of EHV infection in
the autumn-winter period. Infection is carried and spread in aerosol droplets in
the breath of horses which have incubated the virus or are harbouring the virus
as a ‘carrier’ in their throat tonsil area. ‘Carrier’ horses may not exhibit any
signs of respiratory disease, but they can redevelop the infection if stressed by
training, sickness, poor feed, heavy worm burdens or wet, cold conditions.
Thankfully, the Equine Influenza (EI) virus was eradicated after the
outbreak in 2007, as this is a much more aggressive respiratory virus
with potential for severe airway damage and long term side-effects.

DIAGNOSIS OF A COLD
The typical signs of a nasal discharge, reduced appetite and an
occasional cough, develop between 4-6 days after the initial
infection with EHV once the virus has multiplied and
has triggered an immune reaction and increased airway
cleaning mucus and fluid within the lungs.
Monitoring the horse’s temperature first thing each
morning and again in evening before the night feed,
will help identify the infectious nature of the ‘stable virus’
with a body temperature above 38.4-39°C. Examination with a
stethoscope under the throat latch area and upper windpipe may help to
determine increased upper airway ‘noise’ due to the constriction of the upper
airways as a result of inflammation and strands of mucus build-up. In most
cases, except where lower airway reaction with increased mucus streaming up
the windpipe and partial airway constriction may result in airway resonance
when breathing or a slight wheeze, which is aggravated by light exercise, often
lung sounds and the respiratory rate or breathing ‘effort’ are not increased.

YOUNG HORSES
Most young horses develop a ‘head’ cold with a runny nose, coughing and a
‘sore throat’ which reduces their appetite. This is due to increased upper airway
mucus, tonsil reaction and occasionally mildly swollen glands under the rear
angle of the jaw resulting from increased lymph drainage and inflammatory
immune related reaction. If these symptoms are not recognised, and the
animal rested up or treated and managed early in the infective stage, lower
airway reaction and Inflammatory Airway Disease (IAD) can develop within 5-
7 days. This is often a complication in race horses, with up to 65% developing
IAD if early symptoms are not recognised, which is aggravated by inhaled cold
air during early morning fast exercise.
Older horses often develop more chronic Reactive Airway Disease (RAD)
which affects their exercise tolerance and results in a chronic low grade airway
reaction, increased fluid and mucus accumulation and a deep ‘moist’ cough
when exercising.

MANAGING A COLD
It is most important to recognise the symptoms (Refer to Handy Hint 4) as
early as possible. If the horse has not been infected, a couple of days of rest
will not greatly affect its training schedule, but it will reduce the risk of further
complications and long term chronic airway disease if it really has a viral or
other airway infection.
1. Monitor the horse’s temperature and appetite daily.
2. Ensure that the horse is provided with shelter and a warm rug.
3. Separate it from other horses in the immediate vicinity - especially in stables and
yards where horses can come into nose contact through a wall or over a fence.
4. Place all feed on the floor - dampen all feed, including hay (Refer to Handy Hint
6) to assist nasal and throat drainage. Damp feed will be less likely to irritate an
inflamed tonsil or throat and it will often help to encourage the appetite.
5. Only remove patches of wet and soiled bedding and replace with slightly
dampened shavings or sawdust to reduce dust. Try to avoid straw bedding
as this is more likely to contain minute mould and dust particles which can
be inhaled into the lower airways.
6. Cease exercise for at least 48 hours to reduce the risk of lower airway insult
with virus particles - if the horse recovers, re-introduce light exercise after
3-4 days, but maintain below chest height, floor feeding.

AIDS TO ASSIST RECOVERY FROM THE STABLE VIRUS
There are a multitude of preparations, many of which are similar to
medications for human ‘coughs and colds’, that are available for horses.

ANITBIOTICS, BRONCHODILATORS AND MUCAS CLEARING PREPARATIONS
These preparations are only available from your vet and are usually only
prescribed following a clinical appraisal of the horse’s respiratory function and
perhaps a scope of the lower windpipe area to determine the amount or number
of strands of mucus accumulated in the lower part of the windpipe. A Broncho
Alveolar Lavage (referred to as a BAL or ‘lung wash’) may be collected by passing
a special BAL tube down the windpipe into the rear end of the lung bronchi,
injecting 60ml of saline and collecting a representative wash of the lower airways and examining the wash fluid for types of cells, such as monocytes (scavenging
cells), lymphocytes (cellular immune cells), eosinophils (allergic reaction cells) and
red blood cells (lung bleeding during intense exercise) and mucus content.
A BAL is not an accurate means of culturing for airway bacterial infection due
to the high degree of contamination of the lower airway with microbes and
dust from inhaled air. The horse may be prescribed antibiotics as a precaution
against secondary infection, which is a common problem following respiratory
viral infection, as it is in humans.
Mucolytic agents (they act to liquefy thick mucus in the throat and lower airways)
and bronchodilators (they act to relax constricted airways to facilitate breathing
and mucus drainage) - they are often combined together, and can help to facilitate
expulsion of thick mucus from the lower airways by head-down airway drainage
when feeding or grazing. They may be beneficial to hasten recovery if a horse
has accumulated airway mucus or a runny nose or sticky, thick snot in its nostrils.
Consult your vet for advice on the selection, dose rate and treatment time relative
to the type, secondary complications and response to the therapy.

COUGH PREPARATIONS
There are a number of cough elixirs (thick sugary flavoured syrups which stick
to the throat membranes and soothe the throat to reduce irritation and the
stimulus to cough), just like the over-the-counter cough medicines available for
humans. These can help relieve a ‘ticklish throat’ and clear away excess mucus.
The problem is that horses are unable to spit out mucus from their mouths as
they have a long soft palate which prevents them breathing, coughing up mucus
or vomiting through their mouth - they do not have stomach vomiting muscles
anyway, as vomit would otherwise be expelled through the nostrils! With head
-down feeding some of the coughed up mucus may be expelled through the
nose as a discharge, or swallowed to be digested and rendered harmless.
Some contain a cough suppressant; others contain an expectorant to help make
coughing more productive by thinning and expelling mucus. However, as is the
case in humans, there are concerns that by suppressing the cough reflex, the
horse may be unable to clear the throat and lower airways. On-ground feeding
with the head down greatly assists lower airway drainage and is likely to be of
more direct benefit in most horses.

MENTHOL GELS UP THE NOSE
Menthol and camphor are popular aromatic compounds which are inhaled up
the nose to help reduce nasal irritation, membrane swelling and oedema and
clear the airways as in human inhaled decongestants as ‘flu’ remedies. Inhaling
menthol vapours by adding a menthol ‘cooling’ gel or Vicks Vaporub® to hot
water and positioning it in a bowl under a horse’s nose for 5 mins 2-3 times
per day when it is tied to a rail, or added to a nebulizer unit, is considered to
be beneficial in clearing the airways. However, both menthol and camphor are
prohibited substances in racing and show horses and must be withdrawn 144
hours before competition. Consult your vet for withdrawal times.

IMMUNE AIDS
A number of injectable immune stimulating agents are available and may
be recommended by your vet to assist the immune status of a young horse,
a horse in hard work with a low white blood count or an aged horse where
immunity may wane with increasing age or an associated loss of weight and
ill-thrift condition on a pasture based diet.
There are also some nutritionally based immune support preparations. These
often contain herbs, vitamin C, Vitamin A and Vitamin E, zinc and selenium
to ‘feed’ the immune system with nutrients required for antibody synthesis and
general well-being. Kohnke’s Own Activ-8 contains bioflavanoids (Vitamin C like anti-oxidants)
organic zinc, organic selenium, Vitamins A, C and E and other immune
support nutrients. Extensive field trials carried out on 100 horses with
symptoms of viral respiratory disease, including EI, indicated that it had a
role in supporting the immune system. A 21 day in-feed course is widely used
to support the immune system of horses with respiratory disease. It is used
by owners of horses travelling to shows and competition, or long distance
transport, as they have observed that it has a beneficial role in immune support
of horses at risk of developing respiratory conditions.

GARLIC POWDER
Garlic is widely touted as an immune boost nutrient, but although it may have
benefits as a natural insect repellent when given daily during the biting insect
season, it has not been credited with assisting the immune system of horses at
the dose rates (20g daily) as often recommended.
Trials have shown in race horses that 20g or more of garlic daily in the feed
can increase the formation of Heinz bodies in red blood cells and dramatically
reduce their lifespan in the blood, thereby resulting in a relative anaemia from
red cell loss. It is not recommended for performance horses for this reason.

ECHINACEA
Echinacea is claimed to support the immune system in humans, but in carefully
controlled trials in Canada, it was found to have no benefit at all in horses at
commonly recommended dose rates in feed or supplements.

VITAMIN C
Vitamin C has a role as an anti-oxidant in the blood and muscles during
exercise to regenerate Vitamin E and early studies in humans suggested that
high doses assisted the immune response and reduced the severity of flu-like
symptoms. The average healthy horse synthesises about 21 grams of Vitamin C
from glucose in its liver each day to meet its needs - humans, apes, reptiles and
birds are unable to synthesize Vitamin C and need a daily source in food. It is
considered that Vitamin C could benefit the immune system when given with
other immune support nutrients, especially in aged horses and pregnant mares,
which may have lower blood levels of Vitamin C.
Herbs containing Vitamin C, such as Rose Hips - they contain 112mg Vitamin
C per 20g dose when freshly harvested and about 20mg iron (a horse needs
350mg iron per day) are unlikely to have any nutritional benefit to support the
immune system.

VACCINATION
A vaccine has been developed in Australia and is available from vets for
the immunisation against EHV. It is recommended for horses which travel
frequently or are exposed to EHV infections on agistment farms, breeding
farms and show competition. Consult your vet for advice on the benefits of
EHV vaccination.

Article courtesy of Dr John Kohnke BVSc RDA - Talking Horses newsletter