Respiratory Conditions in Horses

By Jean Hofve, DVM

Introduction

Horses, for all their size and power, are delicate, sensitive animals. For sport horses and other equine athletes, the difference between a great performer and a disabled pasture pet can be a very fine line. While physical injuries, and ailments like colic, are easily recognizable, signs of respiratory disorders can be very subtle, especially in the early stages. Yet, respiratory disease can have as much or even greater impact on the horse’s well-being and performance than many more obvious problems.

Table of Contents

1. The Equine Respiratory System2. Which Horses Are at Risk?3. How Airway Disease Develops4. Extreme Airway Disease – COPD5. Conventional Treatment 6. Environmental Management 7. Is There a Holistic Alternative?8. Funtumia elastica 9. Preventing Respiratory Disease10. Glossary11. References12. Copyright Information

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1. The Equine Respiratory System

The intake of air starts at the nostrils and moves through a network of thin bones called turbinates. From there, it moves through the sinuses and into the main airway, the trachea. The lower end of the trachea splits into two branches (one to each lung), which then subdivide many times until reaching the air sacs in the lungs where oxygen can be transported into the bloodstream.

The respiratory system resembles an upside-down tree, where the nostrils are the roots, the trachea is the trunk, and the branches (airways) multiply and get smaller (from large bronchi to tiny bronchioles) until reaching the leaves (air sacs), where gas exchange with the air takes place.

Figure 1. The horse’s airways are lined with mucous membranes and small hairs called cilia. The cilia move, or “beat,” upwards and outwards to propel small particles away from the depths of the lungs. These normal defenses help keep the lungs safe and healthy.

The respiratory tract is lined with specialized cells that perform many functions. The nostrils are lined with skin, which becomes a moist mucous membrane as it progresses inward. Olfactory cells that sense odor are numerous in the turbinates. Much of the tract is also lined with cilia (tiny hair-like projections; see Figure 1). The nasal passages and sinuses warm and moisten the air as it flows toward the lungs, while the mucus and cilia trap small particles. The cilia move rhythmically to move mucus and particles upward and outward. The horse will then blow (snort) or cough to force these particles out of the system.

Infection-fighting white blood cells are also found along the respiratory tract as well as deep inside the lungs. These cells are crucial for defense against viruses, bacteria, and other organisms. However, they also cause inflammation that, left untreated, can lead to development of serious lung disease.

2. Which Horses Are at Risk?

The classic picture of risk is a mature horse (usually 6 or older) who is stabled during the winter. However, any horse can develop airway inflammation that can progress to serious disease over time.

While it is always essential to watch your horse for subtle signs of illness, it is also important to understand that significant airway disease may be present long before obvious symptoms occur. In one study, 100% of sport horses of all ages, housed in a conventional stable—although they appeared perfectly healthy, were performing well, and had no outward signs of lung problems—had microscopic evidence of inflammatory airway disease.1

This suggests that any horse can develop respiratory problems. Housing, feed, bedding, weather, and activity are all factors that influence the risk for any individual horse. Horses involved in high-intensity activities are particularly susceptible, especially if they live, train, or work in cold-weather conditions.

Breeds and activities that are at risk include:

Cold weather itself may be a significant problem for many horses. Exercising in frigid temperatures has been shown to cause inflammation in the lungs and airways, and may be a large factor in the development of respiratory infections and asthma.2 3 4

Signs of respiratory problems include poor performance, tiring more easily, taking longer for breathing to return to normal after exercise, increased breathing rate or effort, increased nasal mucus, increased snorting, coughing, and wheezing.

3. How Airway Disease Develops

Sport/Working Breeds

High-Intensity Activities

Andalusian DressageArabian DrivingFriesian EnduranceHanoverian EquitationHolsteiner Fox HuntingMorgan JumpingOldenburg RacingPeruvian Paso/Paso Fino

Rodeo

Standardbred RopingThoroughbred SteeplechasingTrakehner Three-Day EventingWarmblood Western Riding

Equine respiratory diseases are usually environmentally based. Allergies to dust, mold, mites, or other airborne particles frequently occur. Hay and straw are the most common sources of these particles.

When mold spores, pollens, mites, or other particles are inhaled, the respiratory lining cells secrete mucus to try to lift and discharge the particles, thus stimulating the horse to blow them out (snort) or cough.

Respiratory allergies develop when the horse inhales certain particles, including dust and storage mites, molds, and pollens, and the immune system reacts extra-strongly to them. Some allergies are present from birth, but others develop over time, with chronic exposure. This is why problems are seen most often in older horses.

When airborne allergens get down into the airways, they irritate the cells and cause mucus secretion, which will trigger a snort or cough. However, if the horse is allergic to one or more of these particle types, inhaling them will also cause inflammation. Large numbers of white blood cells move into the area. Some of these cells secrete chemicals that cause swelling. Others produce antibodies to the allergen(s); this causes even more inflammation. Because of the mucus and inflammation, less air can get through. To make matters worse, smooth muscles in the walls of the lower airways constrict to prevent the allergens from passing further down into the lungs. This reduces the amount of total air space in the airways and lungs. Wheezing and coughing occur, which then worsen the irritation and inflammation in the lungs. It is a vicious circle in which the body’s own defenses ultimately cause the most harm. (See Figure 2.)

Figure 2. A normal airway is a tube with a smooth inner surface where the air passes through. An inflamed airway’s lining

swells, small muscles constrict the tube—creating an uneven surface that causes disruption of air flow—and mucus accumulates, making the diameter even smaller, with less room for air to reach the body.

With mild allergies, symptoms may seem minor (or may not even be noticeable), and not affect the horse’s performance; but the problem tends to get worse over time. Therefore, it’s best to take preventive action early—before the allergic reaction gets worse.

It’s worth noting that every exposure to the allergen causes inflammation that lasts for days, so horses that are outside during the day and only exposed to dust and allergens in the stable at night or in the arena are still at risk.5

4. Extreme Disease – COPD

A very serious equine lung disease is “Chronic Obstructive Pulmonary Disease” (COPD), also called “heaves” or “broken wind” due to the labored breathing that occurs as the disease progresses. It is often called “Equine Asthma” because it is similar to asthma in people. Other terms for the same syndrome are “Reactive Airway Disease” (RAD) and “Recurrent Airway Obstruction” (RAO). COPD accounts for half of all lung diseases seen in performance horses.6

COPD is on the extreme end of the respiratory allergy scale. It is most likely to develop in colder climates, and in horses over age 6 that are stabled in the winter rather than pastured. A stable is usually a dusty place, and that dust can contain many allergens. Straw bedding and hay are primary sources of a wide variety of allergens. When a horse is breathing this dust for hours at a time, problems can arise. The most commonly implicated allergens in COPD include Aspergillus, Penicillium, and other molds.7 Even clean hay contains small amounts of mold, dust mites, pollen, and other debris; moldy hay, of course, is even more contaminated. If conditions are humid or damp, bacteria and mold in the hay can grow. (See Figure 3.)

Figure 3. U.S. mold spore distribution on a typical June day.

In COPD, the allergic reaction is extreme and chronic. Massive numbers of white blood cells accumulate, and the airways become clogged by swelling, cells, and mucus. Eventually, the airway walls and air sacs become so thickened and scarred that they lose their flexibility, and can no longer expand and contract normally. The bronchial muscles go into spasm. Mucus, cells, and particles collect in the airways, shrinking the air passages even further. The lungs lose elasticity, function, and volume. The horse has a hard time getting air in and out of his lungs, and must use his abdominal muscles to force air out during exhalation. This is what causes the classic “heave line” seen in severe cases of COPD (see Figure 1). In this phase, it is similar to human emphysema. Airway constriction, irritation, inflammation, and mucus all contribute to COPD.

However, even horses on pasture can sometimes become allergic to certain molds or pollens and develop “Summer Pasture Associated Obstructive Pulmonary Disease (SPAOPD).” About 10% of COPD horses also have SPAOPD.

Excessive nasal mucus and coughing are classic signs of equine asthma. However, one of the most common early signs is decreased or poor performance.8 A horse with advanced COPD may suffer considerable respiratory distress. The typical asthmatic cough sounds long, deep, and hollow. Breathing is often labored and wheezy. The

nostrils may be flared to draw in more air. In severe cases, even the slightest activity can bring on an episode of coughing and wheezing. Obviously, these horses can no longer work.

5. Environmental Management

Environmental management is the first step in treatment. Make sure the barn has excellent ventilation, and keep doors, half-doors, and windows open as much as possible. If the weather is cold, it is better to blanket the horses than to close off sources of fresh air. Good hygiene (frequent removal of damp or soiled bedding) is also important.

A horse with COPD may need to be fed pelleted feed rather than hay. Some studies suggest that silage may be a good alternative to hay, but silage molds easily due to its moisture content, and there have been cases of botulism in horses from silage. One study showed that hay that was thoroughly soaked in water produced less dust and appeared safer to feed. Rolled grains should be limited due to their high dust levels.9 All feeds should be as clean and as high quality as possible.

While stalls are being cleaned, the horse should be removed to an outdoor run or other secure area until the dust settles. Hay for other horses in the barn should be stored away from the stables and kept as dry as possible. Hay stored in the same barn with COPD horses was shown to rapidly cause heaves symptoms and worsening of lung function. Wood shavings, shredded paper, or rubber mats should be used for bedding instead of straw, to minimize dust; good quality straw may also be less dusty.10

Indoor riding arenas can be extremely dusty.11 Exercise in cold weather should also be avoided. Although some exercise is good for these horses, dusty conditions or extreme cold can severely aggravate symptoms after even moderate exercise.12

6. Conventional Medical Treatment

Conventional medical treatment generally includes anti-inflammatory steroids and bronchodilators to reduce the muscular spasms in the lungs. While symptoms may resolve temporarily, these drugs have serious side effects including laminitis (founder), and they suppress the immune system, making the horse more susceptible to viruses and other infectious diseases. Inhaled steroids deliver a smaller dose to a more focused area, but require daily or twice-daily administration using a special mask. Conventional drugs may not be suitable for long-term management of the problem because of potential side effects, or because they contain prohibited substances under the rules of various equine sport governing bodies.

7. Is There a Holistic Alternative?

Fortunately, there are holistic treatments that are safe and gentle. Essential fatty acids, with their antioxidant and healing properties, are one such option.

Herbs can be a safe, effective alternative to drugs for COPD. Properties of the ideal herb for this condition would include:

Antioxidant, to reduce inflammation-causing molecules in the body that contribute to asthma13

Antifungal, to inhibit mold particles that commonly cause COPD14

Immune-modulating, to decrease the over-reactive immune response to allergens

Anti-inflammatory, to protect the lungs from the harmful effects of inflammation

Free from heavy metal contamination, to prevent toxic build-up Contains no prohibited substances Safe—of course!

8. Funtumia elastica, a Traditional Asthma Remedy

Funtumia elastica is a medium-sized African rubber tree with glossy leaves, milky sap, and long woody seedpods. The bark is the medicinal portion. Scientists studied Funtumia extensively in the 1960s, but only recently have its medicinal properties recaptured the interest of science. Funtumia elastica has important antioxidant, antifungal, anti-inflammatory, and antibiotic properties. It is traditionally used in its native environment, tropical Africa, to treat asthma, allergies, and other respiratory issues, as well as malaria. It has no known toxicity, and is not barred by any equine sport governing body.

Natural compounds found in Funtumia elastica include:

Anthocyanins : plant pigments that give berries their color (such as blueberries, blackberries, and cherries). Anthocyanins have been called “the mother lode in a gold mine of antioxidants.” Unprocessed Funtumia elastica powder is distinctly blue—a clear indication of its high anthocyanin content. Anthocyanins are powerful antioxidants that have beneficial effects on the heart, brain (enhancing learning and memory), and eyes. They have good anti-inflammatory effects and appear to protect against DNA damage, cancer, and many degenerative diseases. Anthocyanins have shown specific benefit in reducing immune-stimulated inflammation, and are thought to be valuable in preventing the development of asthma.15 16 17

Flavonoids : Vitamin C is the most familiar member of this class of plant-derived antioxidant compounds. Flavonoids are natural antihistamines and posses strong anti-allergic properties. Flavonoids are useful in both preventing and treating COPD, asthma, and other chronic lung diseases.18 19 20

Steroid alkaloids, plant sterols (phytosterols), and brassinosteroids: natural plant steroids are safer than synthetic steroid drugs like prednisone and dexamethasone. One compound (conessine) found in Funtumia also has strong anti-bacterial properties.21 Phytosterols have immuno-modulating effects—normalizing an over-reactive antibody response—as well

as anti-inflammatory and anti-cancer properties. Interestingly, in a study of marathon runners using a blend of phytosterols, volunteer runners taking the blend had a smaller inflammatory response and less immune suppression during recovery. Their effects on immune system balance are thought to be beneficial in treatment of allergies and other autoimmune conditions. 22 23 24 25

1 Gerber V, Robinson NE, Luethi S, et al. Airway inflammation and mucus in two age groups of asymptomatic well-performing sport horses. Equine Vet J. 2003 Jul;35(5):491-5.2 Davis MS, Malayer JR, Vandeventer L. Cold weather exercise and airway cytokine expression. J Appl Physiol. 2005 Jun;98(6):2132-6.3 Davis MS, Royer CM, McKenzie EC, et al. Cold air-induced late-phase bronchoconstriction in horses. Equine Vet J Suppl. 2006 Aug;(36):535-9.4 Davis MS, Williams CC, Meinkoth JH, et al. Influx of neutrophils and persistence of cytokine expression in airways of horses after performing exercise while breathing cold air. Am J Vet Res. 2007 Feb;68(2):185-9.5 Davis MS, Williams CC, Meinkoth JH, et al. Influx of neutrophils and persistence of cytokine expression in airways of horses after performing exercise while breathing cold air. Am J Vet Res. 2007 Feb;68(2):185-9.6 Dixon PM, Railton DI, McGorum BC. Equine pulmonary disease: a case control study of 300 referred cases. Part 1: Examination techniques, diagnostic criteria and diagnoses. Equine Vet J. 1995 Nov;27(6):416-21.7 Nardoni S, Mancianti F, Sgorbini M, et al. Identification and seasonal distribution of airborne fungi in three horse stables in Italy. Mycopathologia. 2005 Aug;160(1):29-34. 8 Allen KJ, Tremaine WH, Franklin SH. Prevalence of inflammatory airway disease in national hunt horses referred for investigation of poor athletic performance. Equine Vet J Suppl. 2006 Aug;(36):529-34.9 Vandenput S, Istasse L, Nicks B, et al. Airborne dust and aeroallergen concentrations in different sources of feed and bedding for horses. Vet Q. 1997 Nov;19(4):154-8.10 Vandenput S, Duvivier DH, Votion D, et al. Environmental control to maintain stabled COPD horses in clinical remission: effects on pulmonary function. Equine Vet J. 1998 Mar;30(2):93-6.11 Rapp HJ, Weiss R, Bockisch FJ, et al. Studies in riding arenas and on different riding path surfaces with respect to respiratory tract contamination in horses. Air hygiene studies in riding arenas. Tierarztl Prax. 1991 Feb;19(1):74-81.12 Davis MS, Malayer JR, VanDeventer L, et al. Cold weather exercise and airway cytokine expression. J Appl Physiol. 2005 Jun;98(6):2132-6.13 Shaheen SO, Sterne JA, Thompson RL, et al. Dietary antioxidants and asthma in adults: population-based case-control study. Am J Respir Crit Care Med. 2001 Nov 15;164(10 Pt 1):1823-8.14 Woods PS, Robinson NE, Swanson MC, et al. Airborne dust and aeroallergen concentration in a horse stable under two different management systems. Equine Vet J. 1993 May;25(3):208-13.

Natural anti-fungals : Funtumia specifically inhibits growth of many molds, including Aspergillus, Penicillium, Candida, as well as the fungi that cause ringworm.26

Tannins : These compounds, found also in coffee, tea, and red wine, have shown promise in the treatment of allergic inflammation and asthma. Tannins affect the body’s production of prostaglandins (a group of hormone-like substances) by inhibiting pro-inflammatory molecules known to be associated with COPD in horses and promoting anti-inflammatory production. 27 28 Tannins may also help break down foreign proteins, which could reduce the allergic response.29

Funtumia elastica has demonstrated good safety (low toxicity) in multiple laboratory experiments, and has tested negative for heavy

15 Barros D, Amaral OB, Izquierdo I, et al. Behavioral and genoprotective effects of Vaccinium berries intake in mice. Pharmacol Biochem Behav. 2006 Jun;84(2):229-34.16 Park SJ, Shin WH, Seo JW, et al. Anthocyanins inhibit airway inflammation and hyperresponsiveness in a murine asthma model. Food Chem Toxicol. 2007 Aug;45(8):1459-67.17 Zafra-Stone S, Yasmin T, Bagchi M, et al. Berry anthocyanins as novel antioxidants in human health and disease prevention. Mol Nutr Food Res. 2007 Jun;51(6):675-83.18 Kawai M, Hirano T, Higa S, et al. Flavonoids and related compounds as anti-allergic substances. Allergol Int. 2007 Jun;56(2):113-23.19 Knekt P, Kumpulainen J, Järvinen R, et al. Flavonoid intake and risk of chronic diseases. Am J Clin Nutr. 2002 Sep;76(3):560-8.20 Romieu I, Trenga C. Diet and obstructive lung diseases. Epidemiol Rev. 2001;23(2):268-87.21 Bogne Kamga P, Penlap Beng V, Lontsi D, et al. Antibacterial activities of the extracts and conessine from Holarrhena floribunda. Afr J Trad Complem Alt Med. Vol. 4, No. 3, 2007, pp. 352-356.22 Bouic PJ, Lamprecht JH. Plant sterols and sterolins: a review of their immune-modulating properties. Altern Med Rev. 1999 Jun;4(3):170-7. 23 Michelini FM, Ramírez JA, Berra A, et al. In vitro and in vivo antiherpetic activity of three new synthetic brassinosteroid analogues. Steroids. 2004 Oct-Nov;69(11-12):713-20.24 Wagner H, Seegert K, Sonnenbichler H, et al. Steroid alkaloids of Funtumia africana. Planta Med. 1987 Oct;53(5):444-9.25 Zirihi GN, Grellier P, Guédé-Guina F, et al. Isolation, characterization and antiplasmodial activity of steroidal alkaloids from Funtumia elastica (Preuss) Stapf. Bioorg Med Chem Lett. 2005 May 16;15(10):2637-40.26 Adekunle AA, Ikumapayi AM. Antifungal property and phytochemical screening of the crude extracts of Funtumia elastica and Mallotus oppositifolius. West Indian Med J. 2006 Sep;55(4):219-23.

metals including cadmium, zinc, lead, chromium, and nickel. It does not contain any substances that are prohibited by any equine sport authority.

9. Preventing Equine Respiratory Disease

Many factors contribute to the development of respiratory problems in horses. If your horse is stabled—even with plenty of turnout time—the risks are higher. Smart barn management, such as storing hay away from the horses; abundant ventilation; using minimally dusty bedding and feed; and appropriate use of herbs and supplements; can all reduce your horse’s risk.

Equine sports are stressful to the horse’s body, and the immune system in particular, even if the horse enjoys the sport. You want to keep your horse balanced, and ready to handle any stresses that may be lying in wait, whether at the home barn, or at the next stop down the road (especially if you are unfamiliar with their barn practices). After all, an “ounce of prevention” is far better than a lifetime of symptom management and the loss of your horse’s health and athletic abilities.

This Paper is Presented by:

27 Watson ED, Sweeney CR, Steensma KA. Arachidonate metabolites in bronchoalveolar lavage fluid from horses with and without COPD. Equine Vet J. 1992 Sep;24(5):379-81.28 Watson ED, Mair TS, Sweeney CR. Immunoreactive prostaglandin production by equine monocytes and alveolar macrophages and concentrations of PGE2 and PGF in bronchoalveolar lavage fluid. Res Vet Sci. 1990 Jul;49(1):88-91.29 Kimura Y, Okuda H, Okuda T, et al. Studies on the activities of tannins and related compounds, X. Effects of caffeetannins and related compounds on arachidonate metabolism in human polymorphonuclear leukocytes. J Nat Prod. 1987 May-Jun;50(3):392-9.

© 2008 Jean Hofve, DVM. All rights reserved. No reprints or reproductions, including but not limited to printing, photocopying, online posting, and

excerpts, without prior written permission.

For more information on using Funtumia elastica in horses,Please visit http://www.ojibwatea.com and click on Horses.

10. Glossary

Pulmonary: having to do with the lungs.

Chronic obstructive pulmonary disease (COPD): a chronic disease of the lungs that results in decreased airflow, decreased lung capacity, and increased effort in breathing.

Respiration: breathing

Respiratory system: the organs functioning in breathing, including the nose, nasal passages, pharynx, larynx, trachea, bronchi, and lungs.

11. References