Winter Respiratory Issues

with Dr Paula Williams

BSc (Hons) BVSc MRCVS MANZCVS of WestVETS Animal Hospital

As the temperature drops and we head into winter, our horses may show issues related to the season change. Here in Australia, compared to other parts of the world, our climate is quite mild, but in some areas, it really does get colder. In the winter months, horses are more susceptible to skin conditions, hoof problems, certain types of colic and respiratory issues. Just as people have more respiratory problems in the winter months, so too, do horses. Here, we are going to look at some of the respiratory conditions that occur, the clinical signs, how they can be managed and preventative strategies.

Why are there more respiratory issues in the winter?

The cooling of the air is one factor that contributes to respiratory issues. The drying nature of cold air on the mucosal layers of the respiratory tract can affect the local defensive mechanisms. This can, in turn, increase the horse’s susceptibility to irritants and infective pathogens that gain entry via the respiratory tract.

During winter months, horses are often more likely to be housed, and this, too, can predispose to respiratory issues. The air quality in stables and barns is poorer than that outside—there is an increase in the amount of dust, fungal spores, bacteria, endotoxins, and viruses that horses can inhale. Ammonia build-up in stables and barns can also irritate the linings of the respiratory tract. Horses that are housed are in closer proximity to other horses, and this can increase the spread of airborne pathogens.

What are the respiratory issues that occur?

The winter respiratory issues can essentially be divided into two main groups:
Infectious disease (lower and upper respiratory tract)
Non-infectious respiratory disease – equine asthma

Infectious disease
There are many respiratory infections that can occur, some of which have been identified, but there may also be infections that as yet have not been identified.

The pathogens are mainly bacterial or viral and in Australia, include:
• Equine Herpes Virus (EHV)
• Equine rhinitis virus
• Streptococcus species (including strangles)
• There are also other opportunist bacteria that may infect the lower airway
a. Actinobacillus
b. Bordetella
c. Escherichia coli
d. Pasteurella
e. Pseudomonas
f. Rhododoccus (foals)

On occasion, parasites can cause respiratory disease. These include lungworms (Dictycaulus) contracted from donkeys and ascarids, which can cause respiratory disease in younger horses during the migration phase.

Non-infectious respiratory disease of the lower airway
This is inflammation of the lower airway and has many names, including RAO (Recurrent Airway Obstruction), COPD (Chronic Obstructive Airway Disease), IAD (Inflammatory Airway Disease) and now known as EQUINE ASTHMA.
Some studies suggest that 25–80 per cent of stabled horses suffer from equine asthma to differing degrees.

Equine asthma is triggered by inhaled environmental allergens such as dust and fungal spores. These allergens cause irritation of the airways, resulting in hypersensitivity, constriction of the airways and mucus secretion. It is usually a chronic disease with a slow onset, but acute episodes do occur.

What are the signs of respiratory disease?

These signs can be variable depending on the cause. They include:
Dull/depressed
Inappetance
Cough
Nasal discharge
Increased respiratory rate
Exercise intolerance
Poor recovery after exercise
Fever – more common in the infectious causes of respiratory disease

What should I do if my horse is showing these signs?

If infectious disease is a possibility, try to separate your horse from other horses and maintain hygiene to limit the spread of potentially contagious diseases. Stop exercising the horse.

A veterinary evaluation is advised to determine the possible cause of respiratory disease and, therefore, instigate appropriate treatment and management.

What will the veterinarian do?

The veterinarian will evaluate your horse with a full clinical examination, including a detailed evaluation of the respiratory tract. This will include evaluation of the nasal passages, palpation of the larynx and trachea including evaluation of localised lymph nodes, percussion of the sinuses, auscultation of the lungs and heart and taking the temperature of the horse. Normally, the lungs are evaluated at rest and will require a quiet, stress-free environment; on occasion, the veterinarian may lightly exercise the horse or use a rebreathing bag to listen closely to the lung sounds and watch how the horse recovers.

Further diagnostic procedures that may be utilised are endoscopy to visualise the respiratory tract, radiography (this may be used to evaluate the sinuses and sometimes the chest), ultrasonography of the lungs, routine haematology and biochemistry blood tests and sampling of airway discharges and laboratory analysis. Respiratory discharges may be sampled in different ways according to the likely cause of the respiratory disease – these include:

Nasopharyngeal swab
A long swab is placed up the nose, and discharge is collected from the nasal passageway and throat. The sample is then sent for culture and sensitivity to grow bacteria and for respiratory PCR.

Guttural pouch washes
The guttural pouches form part of the upper respiratory tract and may harbour certain bacterial infections. Any discharges from the guttural pouch may be collected by washing the pouch using an endoscope and sampling tube.

Lung washes
Lung washes may be taken to analyse cytology, culture, sensitivity and respiratory PCR. There are two main different types of lung wash - the BAL (Bronchoalveolar Lavage), where a tube is installed into the bronchi, sterile fluid is passed through and sucked back; this is the technique used where equine asthma is believed to be the cause of the issue. The other type is the TW (Tracheal Wash), where sterile fluid is washed into the trachea and then sucked back – this can be performed in two ways, either via an endoscope or using a large needle and small catheter inserted into the trachea externally. The second method is preferable to avoid contamination with upper respiratory flora. The TW is used where infection is believed to be implicated in the lower airway.

What is the treatment?

The treatment is usually a combination of management strategies and medications, depending on the cause of the respiratory disease and the infectious agent (if any) involved.

Management strategies
• Biosecurity protocols - Crucial if a contagious disease is the cause
• Dust free environment
• Stop exercise - Your veterinarian will give you guidance

Medications
The medications used will depend on the underlying cause and severity of the disease. They may include:

• Antibiotics - If there is a bacterial cause, antibiotics will be used. The type selected will depend on the bacteria implicated (ideally from culture and sensitivity) and how sick the horse is. Given the issues with resistance to antibiotics, they should only be used under veterinary guidance and where indicated. Not all coughing horses require antibiotics, and probably many that are treated with them don’t actually require antibiotics. If they are used, they may be administered systemically but also via nebulisation in cases of pneumonia.

• Non-steroidal anti-inflammatory drugs (NSAIDs) - For example, phenylbutazone or flunixin may be used when a horse has a fever.

• Bronchodilators - There may be different types used if there is evidence of broncho constriction. They may be used systemically such as clenbuterol (Ventipulmin or Airway Gel) or via a nebuliser or a puffer.

• Mucolytics - These are medications that help break down thick mucous and include Sputylosin (Dembrexine).

• Corticosteroids - These may be used in cases of equine asthma and may be administered systemically or via a nebuliser of puffer.

• Inhaled drugs - The use of installing medications directly into the airway is becoming more common. The drugs may be nebulised or used via a puffer and mask. Examples include antibiotics for pneumonia, airway dilators, and corticosteroids for equine asthma.

How do I prevent my horse from getting respiratory disease?

Although there are no guarantees during winter months, there are many strategies that can be utilised to reduce the incidence of respiratory disease. These include:

Keep up to date with vaccinations
In Australia the vaccinations available against some of the infectious causes of respiratory disease are the EHV and Strangles vaccine. (The Hendra vaccine is also available – respiratory disease is one of the many presenting signs of Hendra.) Your veterinarian will help guide you with what vaccinations are required for your horse, taking into account many factors.

Implement biosecurity protocols
We have learned a lot about biosecurity in people since the COVID years and the various types of influenza - we can draw on that knowledge and apply it to horses. We are lucky here in Australia compared to many other countries as EI (Equine Influenza) is not present as a norm here (there was the outbreak in 2007, which was eradicated), but there are other contagious respiratory diseases. I am not suggesting that we should make horses wear P2 masks and use hand sanitiser, but we can apply some of the basic biosecurity measures to our horses. The most basic principles implemented in stables are avoiding potential contamination of feed, water and equipment, insect and animal disease vector control, good hygiene when handling horses and isolation of sick horses from healthy ones. If horses are new to a stable or barn or returning from competition, then keeping them separate/quarantined is advisable.

Ensure good ventilation
There are various mechanisms for maintaining good ventilation in stables, including sophisticated equipment such as ducted dust removal systems. Basic principles, such as allowing airflow by keeping windows and doors open, are instrumental in maintaining good ventilation. It is ill-advised to have manure piles, hay storage, and feed sharing the same airspace as housed horses.

Muck out and clean stables when the horse is out
When mucking out stables, sweeping breezeways, using a leaf blower, or exposing the horse to tractor fumes, considerable dust is created; when performing these daily stable chores, it is advisable to have the horses away to prevent them from inhaling the particles. Let them back in when the dust has settled!

Dust free bedding
The choice of bedding is important, and it needs to be as dust-free as possible. Straw is best avoided as bedding.

Feed horses low down
This helps drainage of mucous from the airways.

Soak or steam hay
Soaking hay for at least 30 minutes removes much of the dust particles. Steaming hay has been shown to reduce the fungal spores. Damp down feed to prevent inhalation of dust. Discard any mouldy feed or hay.

Turn out where possible
Air quality is better outside.

Summary

As the temperature drops and more horses are housed, we tend to see more respiratory issues in our horses. Such respiratory diseases include infectious causes and equine asthma. If your horse is showing signs of respiratory disease such as coughing, high temperature, nasal discharge, and poor exercise tolerance, then engage the services of an equine veterinarian so that the horse can be treated promptly and appropriately. If your horse needs to be housed during the winter months, take a look at its environment and ensure the best air quality possible by making a few management changes.

Paula qualified in the UK in 1993 and has been an equine veterinarian since then. She completed an internship at Rossdale and Partners in Newmarket, UK and has subsequently worked in equine hospitals both in the UK and Australia. Paula is currently an equine practitioner at WestVETS Animal Hospitals in Queensland. Her clinical interests include diagnostic imaging, the investigation and management of musculoskeletal issues in the equine athlete, the equine foot, neonatology and internal medicine.