During winter months, viruses are more easily spread and the horse's immune system may be compromised by the stress of cold weather.
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.
In addition, horses spend more time in the stable, sometimes in close proximity to other horses, and if one horse catches a cold bug, it can easily be passed to others.
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 harboring 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.
Diagnosing a cold in your horse
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.
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 your horse's 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.
- Monitor the horse’s temperature and appetite daily.
- Ensure that the horse is provided with shelter and a warm rug.
- 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.
- 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.
- 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.
- 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.
This is a reprint of a previously posted article.