Breathe Easy: supporting you horse's respiratory health
By Dr. Stephanie Wood (Ph.D., PgDip., BSc (Hons), RNutr, R. Anim. Tech.)
You may have heard that keeping your horse, pony or donkey in a dusty stable or feeding them dusty hay is bad for them, or that pollen from plants and trees can affect some horses and ponies in the spring and summer months causing them to shake their heads and be difficult to ride. These issues are due to the negative effects that dust and pollen have on the respiratory system. Understanding the structure and function of the respiratory system, knowing the different hazards that can cause respiratory issues, and identifying what you can do to support your horse’s respiratory health are key to keeping them happy and healthy.
Structure of the respiratory system
The respiratory system of horses, ponies and donkeys starts with the nostrils, where air enters and leaves the nasal passages. All equines are obligate nasal breathers, meaning that they can only breathe through their nose, and that they cannot breathe through their mouth. This is why their nostrils can open wide when they are working hard, and why observing their nostrils is an easy way of monitoring their breathing. Once air enters the nostrils it flows along the nasal passages and into the trachea (also known as the windpipe). The trachea is a flexible tube that is held open by rings of cartilage. This helps air to flow easily along the trachea. The trachea then branches into two tubes known as bronchi, with one tube entering each of the lungs (horses, ponies and donkeys have two lungs). Each bronchi divides many times into bronchioles until the tubes are very small (Figure 1). At the end of the tiny tubes are air sacs called alveoli which are lined with a network of minute blood vessels called capillaries. The alveoli and capillaries are where oxygen (O2) and carbon dioxide (CO2) exchange takes place.
Figure 1: Structures of the respiratory system.
The air that is breathed in contains oxygen, which is needed by every cell in the body to stay alive. When the air reaches the alveoli and capillaries, the oxygen is absorbed into the blood passing through the capillaries. At the same time substances created within the horse’s body that are not needed (waste substances) pass from the blood in the capillaries into the air in the alveoli. The air is then exhaled (breathed out), removing the waste substances from the body. One of the main waste substances that is removed from the body is carbon dioxide. This process of oxygen going into the blood and carbon dioxide leaving the blood is called gaseous exchange and is vital for life.
The structures forming the respiratory tract are lined with sticky mucus and tiny hair-like projections called cilia. The mucus and cilia trap particles that are breathed in, so they don’t reach the lungs. When horses, ponies and donkeys cough, they remove the mucus and the particles from the airways.
Role of the respiratory system
We known that when equines breathe in they bring oxygen into the body, and when they breathe out they remove carbon dioxide from the body. This is a very important process as without oxygen the cells within the body cannot survive. The muscle cells use a lot of oxygen, so when we ride and ask our horses and ponies to use their muscles to perform exercise, they need to bring more oxygen into the body. This is seen by them breathing faster and more deeply. When resting the average adult horse breathes in about 80 litres of air each minute, but when exercising this can increase to 180 litres of air per minute, showing how important having a healthy respiratory system is.
The respiratory system also has an important role in keeping our horses healthy as it is part of their immune system. When horses breathe in, the air often contains dust particles or pollen from plants but can also contain pathogens such as viruses or bacteria. The particles can irritate the respiratory system and pathogens can cause infection. The mucus and cilia help to trap and remove the particles and pathogens, but there is also a response from the horse’s immune system to stop infections developing.
Causes of respiratory issues
If horses, ponies or donkeys breathe in too many particles or pathogens the protective mucus, cilia and immune responses may become overwhelmed. Dust, moulds, and pollen can lead to equine asthma (previously called recurrent airway obstruction [RAO] and chronic obstructive pulmonary disease [COPD]) due to the particles physically irritating the trachea, bronchi and lungs.
The most common signs of respiratory issues include:
- Coughing
- Thick green, yellow or creamy discharge from the nostrils (clear discharge is normal)
- Breathing more quickly when resting (normal is 8-16 breaths per minute for horses and ponies, 12–28 breaths per minute for adult donkeys)
- Reduced ability to perform exercise
- Poor body condition
- High temperature (normal 37.5oC–38.5oC for horses and ponies, 36.5oC– 37.8oC for donkeys)
The hygiene of the environment the animal lives in is key to reducing the risk of respiratory issues developing, and in managing them if they already have respiratory problems. Particles that are microscopic (less than 5 microns) can reach deep into the lungs and cause irritation, so it is important to reduce the number of particles in the air the horse, pony or donkey breathes. Within the stable, dust particles from bedding, especially straw bedding, and from forage and feed are known to irritate the respiratory system. Dust is also created when grooming, especially in wet conditions when they are often covered in dried mud. Bedding, forage and feed can also be sources of moulds, bacteria and their toxins, which can reach the bronchi and lungs if inhaled.
Once inhaled, the particles and pathogens irritate the lining of the airways leading to an immune response. The immune system responds by increasing the amount of mucus produced in the bronchi and bronchioles. This extra mucus is not as easy for the horse to remove and so the bronchioles become bunged up with mucus and narrow, meaning that less oxygen can get into the body. This leads to rapid breathing when resting and not being able to reduced exercise tolerance.
Management options to reduce the risk of respiratory issues
When your horse, pony or donkey is stabled, you can take action to protect their respiratory health by reducing the particles in the air within their breathing zone (Figure 2). The breathing zone is the area directly around the nostrils. A reduction in particles in the general environment is ideal, but special attention should be given to the level of particles in the breathing zone.
Figure 2: The horse's breathing zone is the area around their nostrils, shown by the yellow circle.
The following management practices will help you to achieve a low-dust environment:
1) Increase time out of the stable. Where possible and safe for your horse, pony or donkey, it is best to let them spend as much time outside where the air is constantly moving and there will be fewer particles. If this is not possible (due to them being injured or ill, or bad weather), try to have a well ventilated stable so there is always a supply of fresh, clean air for them to breathe.
2) Avoid using straw bedding if possible as it is known to increase respiratory issues as straw can contain moulds such as Aspergillus if it is damp or wet when baled. If straw must be used ensure it is dry and mould free. Alternatively, use dust-extracted shavings, paper, or pellets.
3) Keep the stable clean by removing dirty bedding regularly. Ammonia (the strong smell you get from urine) makes respiratory issues worse. When mucking out, cleaning stables and adding fresh bedding, remove horses, ponies and donkeys from the stable as the ammonia levels will increase and the air will contain lots of particles due to movement of the bedding.
4) Feed only good quality forage and feeds. This means that you should not be able to see any mould on the forage or feed, and it should smell fresh and clean and not musty and damp. If possible, test your forage for moulds and yeasts.
5) Avoid feeding dry hay if your horse, pony or donkey is known to have respiratory issues. If you do have to feed hay it should ideally be steamed to remove the dust, moulds, bacteria and toxins, although most people don’t have a hay steamer. Instead, you can soak the hay to reduce dust levels, with soaking for 1 - 2 hours in warm water shown to be effective.
6) Think about how you feed your horse, pony or donkey as this can also affect the number of particles in their breathing zone. When eating from a haynet they tend to push their noses into the haynet and drag out the forage, causing particles to be disturbed and breathed in. A better option is to feed forage from the floor or a forage feeder that allows them to eat with their head in a lowered position (Figure 3). By eating with their head low, the nose is above the level of the forage and the number of particles in the breathing zone is much lower. Eating with a low head position also encourages the particles trapped by the mucus and cilia within the respiratory system to drain out of the nostrils, helping to protect the lungs.
7) Always give bucket feeds that are damp. When eating out of a bucket the air in the breathing zone is contained by the sides of the bucket so dampening the feeds reduces the number of particles breathed in as the particles are stuck to the feed and not in the air.
8) Avoid grooming and clipping in the stable if you can. By doing such tasks in a more open space the air that is breathed will be constantly moving and contain fewer particles.
Nutritional support for respiratory health
Adding certain nutrients to your horse’s, pony’s or donkey’s diet is another excellent way to support their respiratory health.
Herbs have been used traditionally to stimulate the removal of mucus and particles from the respiratory tract, and to soothe the respiratory lining. Liquorice root, Thyme, Coltsfoot, Marshmallow and Sage can all help to reduce coughing as they relax and soothe the respiratory tract. Thyme also helps to ease breathing as it helps to open up the airways, whilst Liquorice root, Garlic and Oregano help to remove excess mucus.
Reducing inflammation within the respiratory system is also helpful when managing respiratory issues. Herbs such as Lemon peel, Elder flowers, Coltsfoot, and Liquorice root have anti-inflammatory properties, making them excellent additions to the diet.
Another option to help reduce inflammation is to feed essential fatty acids. Essential fatty acids must be provided in the diet (that’s why we call them essential) and summer grass is an excellent source of them. However, some horses, ponies and donkeys do well if fed extra amounts in the form of omega 3 fatty acids. Omega 3 fatty acids are used by the body to reduce inflammation and so are ideal for feeding to those with respiratory issues.
Take home messages
Ø Get to know your horse, pony or donkey’s normal resting respiratory rate so you can spot early signs of respiratory issues (practice counting the number of breaths taken in a minute when they are resting - one breath is taken each time their nostrils open wider)
Ø Make checking nostrils for any thick, coloured discharge part of your daily routine
Ø Never feed mouldy forage or feed
Ø Feed forage from the floor or a low feeder if possible
Ø Dampen bucket feeds
Ø Give your horse, pony or donkey as much time out the stable as possible (and is suitable for them)
Ø When mucking out and adding fresh bedding from them from the stable
Ø Try to groom outside the stable
© Equine Science Academy Ltd 2025. The information contained herein is provided for information purposes only; the contents are not intended to amount to advice and you should not rely on any of the contents herein. We disclaim, to the full extent permissible by law, all liability and responsibility arising from any reliance placed on any of the contents herein. .
If you would like to check your horse, pony, or donkey’s feeding programme is suitable then take a look at the Feed Review and Nutritional Consultation services available.