Respiratory Health in Horses

Respiratory health is of great importance for all horses, but especially for those who suffer from respiratory diseases such as equine asthma, which may be mild or severe. Symptoms of a respiratory problem in the horse can include:

• Increased breathing rate
• Increased breathing effort
• Coughing
• Nasal discharge
• Poor performance

For horses who are suspected to be suffering from a respiratory problem, it is important to contact the vet to seek an accurate diagnosis and appropriate treatment. However, there are a number of management factors that can be considered to optimise long term respiratory health, which mainly amount to reducing dust exposure for the horse as much as possible. The biggest source of dust for the horse is usually their bedding and forage, so their living environment should be assessed and adapted if necessary. Providing plenty of turnout is often preferable to being kept in the stable as there is naturally more airflow and therefore less dust. For good doers or horses prone to laminitis, using a no-grass turnout area such as a wood chip pen is an ideal alternative, but remember that supplementary forage should still be provided in these situations. Although a form of equine asthma has been observed in horses on pasture, it is thought that this is more likely to be stimulated by pollen or fungal spores and so different management and treatment regimens may be required.

Respiratory health is also important for the performance horse in a high level of work. These horses rely on their lungs to provide the oxygen that enables muscles to function and energy metabolism to occur. If the lungs aren’t healthy, the supply of oxygen may simply not be as good as it could be, and performance could be compromised. When the difference between winning and losing is marginal, taking steps to maximise the horse’s respiratory health and function is sensible.

When can forage be an issue for respiratory health in horses?

Sun dried forages such as hay can contain considerable levels of respirable particles. These are very small particles (less than 5µm in size) that are invisible to the naked eye and are a combination of things that could potentially be harmful to your horse’s respiratory health including mould spores, bacteria, microbial toxins, mite faeces and endotoxins. The amount of such particles in forage can be dependent on factors such as the moisture content and the weather during the conservation period, as well as length and conditions of storage. For example, hays which are not sufficiently dry before being baled are likely to have a much greater content of mould spores. Forages that are dried using hot air have much lower levels of respirable particles – there is more on this in our Forage Replacers Section.

The placement of the horse’s forage provision is also relevant to consider. A study from 2014 on young Thoroughbreds entering race training indicated that feeding hay in a net resulted in higher exposures to respirable and inhalable particles compared to feeding hay from the ground (Ivester et al., 2014). Feeding forage from the floor rather than from a hay net may therefore be preferable for horses with respiratory problems.

It is important to be aware that moulds and other respirable particles cannot be identified by the naked eye (unless present in very high levels). For this reason, it is commonly recommended to feed hay that has been soaked or steamed for horses with respiratory problems, as this has been suggested to reduce clinical signs and support lung function (Westerfield et al., 2024).

How long should I soak my horse’s hay for?

If hay is being soaked for respiratory reasons, then recommendations are usually to soak for between 10 and 20 minutes, although some advocate soaking for up to an hour. The key point though is that the hay should not be allowed to dry out prior to feeding, so once the hay has drained it should be given to the horse. If the horse also requires a low sugar and starch diet due to metabolic or other health problems, then recommendations for soaking duration will typically be much longer. Any soaked hay which is leftover at the end of the day should be removed and discarded.

What’s the alternative to soaked hay?

Since soaking hay is not always practical and can also increase the number of bacteria present, another option is to use wrapped forages such as haylage or wrapped hay, as the wrapping allows a higher moisture content to be retained in the forage which helps to keep dust or respirable particle levels down. Levels of dust will of course vary between different forages depending on environmental conditions during growth, harvest and storage, but research has suggested that respirable dust exposure may be around three times lower when feeding haylage compared to hay (Olave et al., 2021).

However, bear in mind that wrapped forages are often harvested earlier in the year when the plants are at a younger botanical age. This means they can be more digestible and therefore more likely to result in weight gain, and so aren’t always ideal for good doers. Additionally, care should be taken to ensure bale wrappings are not damaged or punctured before being used as this can allow air or moisture to enter the bales and increase fungal growth within the forage. For the same reason, haylage bales should also be fed and used up within a couple of days of being opened. This may make the use of big baled haylage more difficult on yards with only small numbers of horses.

If using wrapped forages is not an option, steaming hay is a way of making it suitable for those with respiratory issues without having to soak it. Steaming has been shown to reduce respirable particle levels by around 70-90%, resulting in significant improvements in respiratory symptoms and lung inflammation (Symoens et al., 2024).

Does steaming reduce the sugar content of hay?

Generally speaking, steaming will not reduce a hay’s sugar content to anywhere near the same extent as soaking. In one study, steaming reduced the water soluble carbohydrate content (WSC; sugars and fructan) by 3% whereas soaking the same hay reduced WSC by around 34% on average (Moore-Colyer et al., 2014). However, steaming has been shown to be more beneficial for the hygienic quality of hay. While soaking increases the bacterial presence, steaming may reduce bacteria numbers by up to 98-99% (Moore-Colyer et al., 2014). Since both methods have their benefits, for horses who need the reduction in WSC content, it is advisable to soak the hay first, and then follow up by steaming it to reduce the bacterial count.

Image courtesy of Haygain

How long should hay be steamed for?

The recommendations for the length of time to steam hay vary according to different manufacturers of commercial steamers. In the study mentioned above, the steaming was for around 50 minutes. If choosing a steamer that advocates a lesser steaming time, it is worth querying what research they have done to show the shorter time frames are adequate, as well as whether the temperature of the steam is sufficient to kill the same level of bacteria. Although shorter steam times may seem more convenient, it is important to compare their performance. Despite the fact that steamers are quite expensive to purchase, their performance cannot usually be replicated by trying to steam hay yourself.

Can I use straw?

For many leisure horses, overweight horses or good doers, straw is a very useful component of the forage ration as it provides fibre without too many calories. However, since straw is sun-dried, mould spore levels can be high. Unless the individual suffers from a respiratory problem though, using straw for horses in light work is not typically an issue, since maximal lung capacity to perform at high speeds is a not the priority. As obesity is generally a far bigger threat to health, it can be sensible to use straw as a source of fibre, especially as it will be lower in sugar in comparison to grass forages – this makes straw particularly beneficial for those prone to laminitis. It is worth noting that straw can also be soaked or steamed to improve its hygienic quality, just like hay. Doing this may also help to soften its structure slightly as well, potentially helping to improve palatability.

Using Forage Replacers

Another option is to use forage replacers that are precision dried. This is a way of conserving forages or fibre feeds that ensures they are as clean as possible. Hot air is blown through the crop in big, but gentle, tumble driers to dry it much quicker than if it were laying in a field in the sun. This drying process involves ‘flash’ drying at high temperatures and essentially locks in nutrients compared to sun curing, where grass for hay is left to dry in the field for days and many nutrients are lost. Precision drying also produces a very clean forage source as any mould spores present are effectively killed by the high temperatures.

An example of a precision dried forage replacement feed from the Dengie range is Hi-Fi Senior which is a short chopped fibre containing dried grass and alfalfa. It can be fed as a total forage replacer, weight for weight in place of hay. These types of product are perfect to feed in a bucket rather than in a haynet. This may provide further benefits as feeding from a lower level (i.e., a bucket placed on the floor) may be beneficial to aid clearance from the horse’s airways. More information on feeding forage replacers can be found here.

Antioxidants

Antioxidants are the body’s natural defence against free radicals or reactive oxygen species (ROS), helping to stop the chain reaction of free radicals that can cause harm. Whilst free radicals can be helpful in small amounts (e.g., when produced by the immune cells to help the body fight against a pathogen), they can cause problems when their production exceeds the body’s antioxidant defence system. This can lead to tissue damage and may be linked to issues such as PPID, muscle problems, joint problems or respiratory disease. Since the horse’s airways are exposed to high levels of stress from pollutants and inhaled allergens, pulmonary oxidative stress can occur and may create problems.

Antioxidants include nutrients such as vitamin E and selenium, so it is really important to supply the horse with a balanced diet. This can be provided by feeding the recommended amount of a nutritionally balanced feed or by adding a balancer or broad-spectrum vitamin and mineral supplement to a chopped fibre feed.

Where can I get more information?

More information and management advice for respiratory diseases in horses is available from the following resources:

• Royal Veterinary College
• British Horse Society

References

• Ivester et al., (2014) Environmental exposures and airway inflammation in young thoroughbred horses. Journal of Veterinary Internal Medicine, 28(3), pp.918-924.
• Moore-Colyer et al., (2014) The effect of five different wetting treatments on the nutrient content and microbial concentration in hay for horses. PLoS One, 9(11), p.e114079.
• Olave et al., (2021) Dust exposure and pulmonary inflammation in Standardbred racehorses fed dry hay or haylage: A pilot study. The Veterinary Journal, 271, p.105654.
• Symoens et al., (2024) Steamed hay and alfalfa pellets for the management of severe equine asthma. Equine Veterinary Journal.
• Westerfeld et al., (2024) Effects of soaked hay on lung function and airway inflammation in horses with severe asthma. Journal of Veterinary Internal Medicine, 38(1), pp.469-476.