Spring allergies - how to treat spring allergies and the effects they have on the respiratory tract

Article by Becky Windell

Spring allergies – peak season of the year-round battle

As obligate nasal breathers horses are predisposed to inhaling respirable dust, mould, pollen and other irritants from the environment. Whilst they have defence mechanisms to deal with it, the horse can be overloaded with the amount they are exposed to. 

Springtime brings an array of newfound pollen from trees, grasses, and crops including the infamous oilseed rape (OSR). This pollen offensive comes in addition to the other allergens in the horse’s environment often surpassing the threshold of irritant load. This can result in respiratory based “spring allergies” with inflammation in the airways leading to allergen based equine asthma. Either subtle signs such as poor performance and reduced stamina will appear and/or more obvious clinical signs such as coughing and nasal discharge1. Horses will tire early due to the reduced amount of oxygen being taken up by the blood from the lungs.

Plants are polyploids and show many gene duplications so cross reactivity among species in which different antigens appear similar to the immune system can amplify the horse’s response to pollen and is particularly the case for grass pollens.2

Generally intact pollen grains range from 10–100 μm in size, this is bigger than respirable particles which are classified respirable at <5 μm. Therefore, pollen has not generally been implicated in Equine Asthma and tends to be considered more of an irritant than allergen. However, a study by White et al identified an association with pollen in a group of horses with Severe Equine Asthma (SEA) while looking at bronchoalveolar lavage fluid (BALF) samples compared to healthy horses2. The effects of pollen on the horse is an area where more research is needed.

Oilseed rape on the decline

It’s well documented that oilseed rape (OSR) is a concern for trainers with some experiencing underperforming horses while surrounding fields are flowering oilseed rape crops. 

Whilst it’s still unclear if there’s truly an allergic component to it, it certainly seems to irritate a lot of horses and vets see pollen in the tracheal washes when OSR is in flower. 

A study in people comparing spring allergy symptoms of people living near OSR and those living far away, found small but significant excesses of cough, wheeze, and headaches in spring in the oilseed rape area3. Interestingly they also found counts of fungal spores were mostly higher in the rape than the non-rape areas so perhaps pollen is not the culprit but fungal spores on the crop…?

This is worth noting as fungi is proven to cause respiratory problems in horses. A study by Dauvillier et al found horses with fungal elements observed on the tracheal wash (TW) cytology had 2 times greater chance of having equine asthma than horses without fungi4. They also found the risk of being diagnosed and likelihood of fungi in TW were higher when horses were bedded on straw or fed dry hay which are key sources of fungi in the horse’s environment.

Practical solutions to OSR have been for trainers to purchase neighbouring fields or pay their neighbouring farmer not to grow the OSR.

From the farmer’s perspective OSR has been an essential part of the arable crop rotation for many years now. It is a crop specially planted to give the cereal crops a ‘break’ from the cycle of weeds, pests and disease that build up in the soil. This helps to improve the yield of the crops that are grown afterwards, such as wheat. 

It used to be good for removing grass weeds too but has become less useful for this purpose in recent years due to weed resistance. In fact, a number of previously positive reasons to grow OSR are no longer standing up. A flea beetle which previously could be treated with a neonicitinoid is no longer licenced for this use, soil borne diseases have become a problem, and the crop does not do well in the wetter winters. 

Ultimately it is now less profitable. This is good news for trainers with farmers starting to use the crop less often and perhaps grow it every 6th year rather than ever 3rd year in a field. Its use is on the decline in UK/Ire and this can been seen in government figures, in 2023-24 all regions in England saw decreases in the oilseed rape area with the largest proportional decrease seen in the North East and the overall decrease of OSR grown in the UK of 27%.5 While in Ireland Winter oilseed rape declined by 30% in 20246. 

Now the interesting question in time is how much will the incidence of spring allergies reduce with the reduction in oil seed rape? 

Global Warming

Dr. Emmanuelle Van Erck Westergren, founder of Equine Sports Medicine Practice in Belgium cautions about the effects of global warming on seasonal allergies. Global warming is altering fungal behaviour and distribution, offering conditions that provide opportunities for fungi such as Apergillus and increases the risk of mycotoxins. In addition the burden of pollen is increased by warming temperatures.

Diagnosing spring allergies

Regular, routine tracheal washes (TW) are useful as a quick and easy “screening” procedure. They help monitor how inflamed the airways are by looking at the neutrophils and macrophage cells. Normal samples are typically of low to moderate numbers of nucleated cells, the nucleated cells being mostly macrophages, with <10% neutrophils. An elevated proportion of neutrophils in the TW is considered to indicate airway inflammation, and cutoff values for neutrophil percentage have been set at 20% for TW.

Ian Beamish partner at Baker McVeigh Lambourn equine practice says he uses the tracheal wash to see “how the army is looking” in terms of number of cells and how many of those cells are dying on the battlefield. 

He also warned “Ultimately, it can be a struggle to determine the actual cause of inflammation of the airways. Whilst spring allergies is a strong possibility at this time of year it could be any number of allergens from the environment causing it or simply the addition of more burdening the system. And then it could also be a virus! It’s important to remember racehorses are immune suppressed from being in full training so they are susceptible to low grade viral disease which can present with similar poor performance.”

To establish if the horse is truly allergic or if it is simply an irritation of the airways there is a diagnostic blood test for allergens. Measuring allergen-specific IgE antibodies present in the serum, can help to identify environmental allergens for both allergen avoidance purposes and to select for inclusion in allergen-specific immunotherapy (ASIT). This can be a helpful aid for diagnosing allergic disease but has been known to give occasional false positives so cannot be relied upon. Establishing the specific allergy is unfortunately very difficult.

Performance Horse Consultant and highly experienced equine vet Peter ‘Spike’ Milligan advises to first and foremost control what you can.

“Reducing contact with pollen can be extremely challenging so first focus on what you can control.  Irrespective of the time of year, regularly re-evaluate the stable environment as well as the forage and bedding quality. This includes how they are stored, prepared and used to ensure the allergen and irritant load is as low as possible.”

A useful tool

The pollen count measures the number of pollen grains in a given volume of air and can indicate if it is a day the horse will be exposed to high concentrations of pollen. Pollen count is affected by the season, weather and even the time of day. The largest concentrations of pollen are found on days of high radiation and wind, early in the morning when pollen is first shed when the air is warming and rising and in the evening as the pollen in the air descends to nose level with the afternoon air-cooling. 

The pollen count can be checked daily on weather apps. Where possible, it’s advisable to adapt the horses training schedule in line with the pollen count and keep training sessions less strenuous on the days the pollen count is high.

Treating spring allergies

Treatment of horses with allergen-induced equine asthma focuses mainly on decreasing and controlling airway inflammation1. The standard and effective cornerstone treatment is to give a systemic or inhaled corticosteroid and if necessary, a bronchodilator can also be used. 

The preferred method to administer these tends to be via a nebuliser because inhaled therapy delivers the drug directly to the lungs and helps to loosen mucous. In addition, a lower dose can be used reducing the chance of side effects and shortening the drug withdrawal time required prior to racing.

Recent advances in treatment include a specifically designed inhaler with a different inhaled steroid, ciclesonide, studies have demonstrated improved clinical signs in a group of horses with mild to severe equine asthma.7,8

However, whilst corticosteroids are very effective and efficient at relieving airway obstruction, they have limited residual effect after treatment stops and long‐term administration is usually limited due to the risk of laminitis, immunosuppression, and interactions with endocrine metabolism9. The drug withdrawal period also impacts the racing schedule. So, what treatments can be used which interfere less with their training and racing plan?

Firstly, creating a barrier between the horse’s airways and the pollen with Nostrilvet or similar and/or the use of a nose-net are low-cost options for training that could be worth a try. This could help to reduce the irritant load on non-race days.

If the horse is truly allergic to certain pollens, then de-sensitisation injections can be used with no withdrawl period necessary. Known as allergen-specific immunotherapy (ASIT) it is a safe long-term treatment which has been used successfully for allergen-induced Equine Asthma. The efficacy of the treatment can vary however, studies suggest that approximately 75% of cases treated showed a good response, with either no need or a reduced need for steroids.

Immunotherapy aims to make the horse tolerant to the environmental allergens that have been diagnosed as responsible for their clinical signs by introducing increasing amounts of the allergen to which they are sensitive. These desensitisation vaccines are administered to the horse subcutaneously. The initial treatment lasts for approximately 10 months, with a dosage regime that gradually increases until the maximum tolerated dose is reached. This is then followed by maintenance treatment. The length of time for a response has been reported to vary between individual horses and can be anywhere from 4 and 12 months. Treatment can be ongoing as premature discontinuation may result in the clinical signs recurring.

Developments in orthobiologics has brought a new non-corticosteroid anti-inflammatory alternative for use in affected horses. Alpha-2-macroglobulin (α2M) is a naturally occurring protein within the blood and is the horses natural defence against inflammation10. Plasma proteins are filtered from the horse’s own blood, leaving an isolated, concentrated alpha-2-macroglobulin product which can be nebulised using a Flexineb. It’s high-priced and still early days for this product but offers a potential drug-free way to treat. It is also an effective anti-inflammatory in joint disease.

Principally the greatest threat to respiratory health year-round is from environmental sources which you can control – the forage, the bedding and the overall stable hygiene environment, this should never be overlooked.

References

1. Couetil L, Cardwell J, Garber V, et al. Inflammatory airway disease of horses— Revised consensus statement. J Vet Intern Med 2016;30:503-515

2. White S, Moore-Colyer M, Marti E, Coüetil L, Hannant D, Richard EA, Alcocer M. Development of a comprehensive protein microarray for immunoglobulin E profiling in horses with severe asthma. J Vet Intern Med. 2019 Sep;33(5):2327-2335. doi: 10.1111/jvim.15564. Epub 2019 Aug 20. PMID: 31429513; PMCID: PMC6766494.

3. Soutar A, Harker C, Seaton A, Brooke M, Marr I. Oilseed rape and seasonal symptoms: epidemiological and environmental studies. Thorax. 1994 Apr;49(4):352-6. doi: 10.1136/thx.49.4.352. PMID: 8202906; PMCID: PMC475369.

4. Dauvillier J, Ter Woort F, van Erck-Westergren E. Fungi in respiratory samples of horses with inflammatory airway disease. J Vet Intern Med. 2019 Mar;33(2):968-975. doi: 10.1111/jvim.15397. Epub 2018 Dec 21. PMID: 30576012; PMCID: PMC6430897.

5. Gov.uk website - Accredited official statistics Cereal and oilseed areas in England at 1 June 2024. Updated 29 August 2024 https://www.gov.uk/government/statistics/cereal-and-oilseed-rape-areas-in-england/cereal-and-oilseed-rape-areas-in-england-at-1-june-2023#:~:text=1.7%20Oilseed%20crops,244%20thousand%20hectares%20in%202024.

6. Teagasc Crop Report www.teagasccropreport.ie Harvest report 2024. https://teagasccropreport.ie/reports/harvest-report-2024#:~:text=The%20area%20of%20winter%20oilseed,of%2021%2C600%20ha%20in%202023.

7. Lavoie J, Bullone M, Rodrigues N, et al. Effect of different doses of inhaled ciclesonide on lung function, clinical signs related to airflow limitation and serum cortisol levels in horses with experimentally induced mild to severe airway obstruction. Equine Vet J 2019;51:779-786.

8. Ciclesonide [prescribing information] Duluth, GA: Boehringer Ingelheim Animal Health USA Inc. 2020.

9. Mainguy-Seers S, Lavoie JP. Glucocorticoid treatment in horses with asthma: A narrative review. J Vet Intern Med. 2021 Jul;35(4):2045-2057. doi: 10.1111/jvim.16189. Epub 2021 Jun 3. PMID: 34085342; PMCID: PMC8295667.

10. Alpha-2 Macroglobulin for the Management of Equine Asthma Summary Results of a Pilot Study Dan Dreyfuss, DVM

Steps to take in order to prevent respiratory disease after a poor harvest

Article by Alan Creighton (Head of environment and nutrition at the Irish Equine Centre)

I don’t want to sound alarmist because I am generally a very positive person, but I have no doubt that there will be an increase in racehorse respiratory issues this winter and next spring due to a combination of poor hay and straw harvests in conjunction with a very damp autumn. 

Through our everyday testing at the Irish Equine Centre we have already seen higher than average fungal contaminated hay, haylage and straw submitted for testing this autumn. Our routine monitoring of racing yard environments in Ireland, the UK and France are also showing increases in fungal contamination in air samples and surface swabs taken throughout the yards. The damp weather conditions from the second week of June right through the summer in western Europe resulted in fields of grass and cereal crops which were showing major signs of fungal contamination while still standing in the field. 

It didn’t get much better when the dry spells came in early September. Land was already saturated which meant the crops once mowed were extremely difficult to dry which has resulted in discoloured, dusty, high moisture straw, many hay stacks which heated and oats with high moisture content. Even haylage, which is the normal go to method of preserving forage when conditions are poor has shown much higher levels of contamination thus far. Damp weather in this period also meant that stables themselves were often damp which encouraged fungal growth on the internal surfaces.

Racehorses are athletes that need a fully functioning respiratory system to maximise performance. IAD, COPD, RAO (all forms of equine asthma) and EIPH (bleeding) are respiratory conditions which are major causes of poor performance in racehorses.  Fungi and mycotoxins are now recognised as a major cause of these conditions and in particular the pathogenic fungus Aspergillus being the main culprit. 

Fungi that penetrate the airways can cause unwanted inflammation and can be infective, toxic, allergenic or all 3 combined. The further the distance a racehorse is asked to race, the more detrimental this inflammation will be to performance. The main sources of this fungus are in hay, haylage, straw and oats. 

This fungus is a storage fungus and so it propagates in stored foodstuffs overtime where the moisture level is above 14%. When the fungus contaminates a foodstuff or bedding the horse has no choice but to breathe in the harmful spores in their stable environment. The fungus also causes a level of immunosuppression which can often be the precursor to secondary bacterial and viral disease. 

The cost of bedding for racehorses has been steadily rising over the last number of years. Wood shavings have become very expensive to buy but are now also very expensive to dispose of. Straw is still more cost effective to buy and much more cost effective to dispose of. 

I will often get asked the question “what is the best bedding for horses?” - my answer is consistently “good straw”. When I get asked the question “what is the worst bedding for horses?” my answer is consistently “bad straw”.  The cost saving in purchasing and disposing of straw has made it attractive to trainers in a time when all other costs are rising. Finding good straw this year will be very difficult. 

In many countries in Europe, we have a government policy called SIM, the Straw Incorporation Measure which is a payment for chopping straw and incorporating it into the soil. SIM has been designed to encourage tillage farmers to increase soil organic carbon levels by chopping and incorporating straw from cereal crops and oilseed rape. 

Unfortunately, an unintended consequence of that policy is the reduction in availability of straw for bedding purposes. This is particularly problematic this year because now we have a shortage of straw and the straw which is available for bedding has much higher levels of harmful moulds due to the poor harvest conditions. 

When feeding haylage, the spoilage process can begin quickly if the bale is exposed to air, this may be due to damage of the wrapping or not using the bale quick enough once opened. Fungal spores will develop and this should be carefully assessed before feeding. This is a major problem we encounter on a regular basis. Often trainers are feeding big bales of haylage to a small number of horses which means the bales are exposed to air for a prolonged period of time. 

Pathogenic fungi will develop very quickly and often lead to both respiratory and gastric problems. For that reason, the IEC will recommend to use haylage once opened inside of 4 days in the winter and 3 days in the summer. This recommendation will often determine the choice between hay and haylage as you would therefore need to be feeding a larger number of horses to feed large bale haylage. 

Hay production requires 7-10 days of continuous good weather unless you are barn drying. In Ireland and the UK we got a two week spell of suitable weather in the last week of May until the end of the first week of June. Many meadows were not ready, and the ones that needed patience from the farmer not to bale too early as hay at that time of the year is very difficult to dry properly due to the lushness of the grass. 

Having said all that, the best hay of this season was made in that period. That was the only spell until a two week spell in September. Historically, the best hay in western Europe is made from the middle of June to the end of July. That was not possible this season. The hay made in that early spell is very good in terms of quality but very poor in terms of volume. The hay made in the second spell in September was very high in volume but very poor in terms of quality. The nutrition levels of this September hay is also poor and the fungal levels are very high.

At the Irish Equine centre we analyse thousands of samples of hay, haylage, chaffs, straw and oats every year for both hygiene (mould and bacteria levels) and nutritional content. The reality is that in a normal year with good spells of weather we still get both hay and haylage with extremely good nutritional and hygiene values and we get hay and haylage with very poor nutritional and hygiene values. 

This year the percentage of poor is outweighing the percentage of good. Normally we would advise that trainers should produce or purchase enough of the same batch of quality forage for the whole season. That may not be possible this year. It is our experience from testing forage that getting haylage with consistent nutritional values can be very difficult even in a good year. This is mainly due to the variants in moisture content which will certainly be the case this season. Hay which is well made and stored well does tend to be much more consistent and therefore better for overall horse health. 

Both hay and haylage are prone to fungal contamination in different ways. With haylage the fungal contamination occurs as a result of inadequate fermentation or when air pockets or punctures occur in the plastic. 

Fungal problems in hay occur because of high moisture levels during the baling process and because of inadequate storage during winter months. We have shown in the past that those fungal problems are compounded and elevated since farmers have moved away from the traditional small bale and moved to large round and rectangular bales. Farmers who traditionally barn dry small square bales, who ensure that hay is dried below 14% moisture and then covered (a layer of clean bales of straw) in storage remains the most hygienic hay for racehorses.

During storage the moisture level on the outside of uncovered bales significantly increases over damp winter months, leading to a significant increase in fungal growth. Round bales suffer the worst during storage. Hay in large bales needs to have a very low moisture level when baling, which just wasn’t possible in most cases this year when field drying. 

When this type of bale has a high moisture level in the centre of the bale it results in significant increases of pathogenic fungi contamination during storage. We have shown through studies that keeping the moisture level of hay below 14% moisture will significantly reduce Aspergillus contamination. It was very difficult to achieve this moisture reduction this summer and often farmers had no choice but to treat the hay with buffered propionic acid which is an effective preservation method which reduces fungal growth during the early stages of storage but its effect diminishes over time.

Good quality tested hay is still the most beneficial to horses when all factors are taken into account. Once purchased hay should be stored properly by the supplier to ensure that it remains consistent. The hay supplier should ideally guarantee the trainer a supply of hay which is consistent for the whole season rather than swapping and changing batches constantly. 

All hay should be covered from the end of September once the moisture content has stabilised to protect it from damp air during winter months. Trainers with inadequate storage may have no choice than to feed haylage. If this is the case, buy the right size of bales for the amount of horses you are feeding. 

Steaming of hay in the correct manner can be a very useful process to reduce the fungal load in contaminated hay. Some producers of hay harvested very early this year to take advantage of that good weather spell. First crop hay when harvested early can be difficult to save and can have a very high protein content. That high protein is good if you test it to quantify the actual protein content and you then balance your feeds accordingly.

If high protein hay or haylage is used and feeds are not adjusted accordingly it can overload the digestive system with nitrogen. Excess of protein will also lead to an over production of urea, leading to an excess of ammonia emissions in the stable which can also cause respiratory irritation.

So, what is the advice from the IEC? Trainers will need to test their hay and haylage at multiple stages during their season as the dangerous fungi will develop over time. The volume of suitable forage and bedding will be low, so trainers should act quickly to secure the best that’s available. 

The nutrition department at the IEC provides full nutritional and hygiene testing for hay, haylage, straw and oats. It is vital that you test forage pre-purchase when trying to buy a season's supply. Hay, haylage or bedding contaminated with pathogenic fungi will cause respiratory disease which will affect racehorse performance. 

For that reason, the cost of testing forage is a small price to pay rather than losing significant portions of the season due to poor performance as a result of respiratory disease. How you store and feed hay, haylage, and oats will have a huge impact on the level of exposure your animals will have to harmful moulds. Stable hygiene and ventilation will be even more critically important when the risk of contaminated inputs is so high.

To conclude, trainers should always acquire the best possible forage and bedding available and test it prior to purchase. You can and should inspect and test any batch of hay or bedding properly prior to delivery. You can take a representative sample for the testing lab which can then be the deciding factor for your purchase. When taking a sample, take a fistful from 6-8 different bales in the stack to ensure you get a representative sample. 

We monitor the stable environments of over 200 racing yards in Ireland, the UK, France and in the Middle East. That monitoring includes hygiene sampling of feed, forage, bedding, water, stable surfaces, walker surfaces and air quality in barns. The benefits of that monitoring for the trainer is that you highlight issues which can cause respiratory disease, proactively prevent disease problems and finally have a mechanism which quantifies the effectiveness of stable disinfection routines. 

The most consistent trainers in terms of performance have good hygiene practices. If anybody would like to discuss the above issues or need help with assessing the quality of forage and bedding in use, please contact myself or any of my team at nutrition@irishequinecentre.ie and we would be glad to help.