A preliminary study suggests that a herbal preparation may be helpful in the management of recurrent airway obstruction.
Recurrent airway obstruction, (RAO) also known as chronic obstructive pulmonary disease (COPD) or heaves, is a common problem of stabled horses. It is caused by inhaled stable dust, which contains agents that cause lung inflammation - including fungal spores, bacteria and endotoxin.
Severely affected animals show signs such as dilated nostrils, nasal discharge, and excessive chest movement. A "heave" line may be present. They may be incapable of any athletic activity. Mild cases may appear to breathe normally and require further investigation to confirm the diagnosis. However, most cases fall somewhere between the two extremes.
RAO is a common cause of poor performance. The respiratory system is one factor that limits maximum
athletic ability, even in healthy horses. When it is diseased there can be a significant effect on performance.
Inhalation of stable dust by a susceptible horse leads to spasm of the airways and increased mucus production. The airway mucus contains an increased number of inflammatory cells (neutrophils).
In many cases, providing good ventilation and putting the horse onto dust-free bedding and feeding haylage may be all that is needed. However, affected horses are often kept at livery stables, where the horse's owner may have little or no influence over the conditions within the stable.
Horses that are more severely affected, and those whose environment cannot be adequately improved, may need medication. Bronchodilators are used to relax the spasm in the airways. Mucolytics thin the mucus and encourage its expulsion. Long term treatment becomes expensive.
There is a growing interest in herbal medications, because of the perception that they are both a less expensive and a more "natural" alternative to the use of pharmaceutical preparations. One such product*, which is a popular treatment for human bronchitis, has been the subject of research at the University of Vienna. Professor René van den Hoven and colleagues in the department of Veterinary Medicine have been assessing its effect on various measures of lung function in horses.\
The preparation contains extracts of thyme (Thymus vulgaris ) and primula (Primula veris ). The principle active constituent is thymol, but there are others including 1,8-cineol, the main component of eucalyptus oil. Thymol is absorbed in the intestines and is excreted through the lungs or in the urine. It relieves spasm in the airways and has anti-inflammatory properties. The other constituents of the extracts also have expectorant and mucolytic properties.
The researchers took five horses known to suffer from recurrent airway obstruction. They made no attempt to improve the environment within the stables for the duration of the trial. The horses were stabled individually but shared the same air space. They were fed coarse mix and poor quality hay. Fifteen tablets of the herbal preparation (each containing 160mg dried T.vulgaris extract and 60mg dried P. veris root extract) were added to the food twice daily.
There was no problem getting the horses to take the tablets. "They ate them within minutes of them being placed on top of the coarse mix" reports Prof van den Hoven.
The researchers used several tests to assess the function of each horse's lungs before and after one month's treatment. They found a significant improvement in lung function (compliance, pulmonary pressure and airway resistance). However there was no corresponding improvement in the severity of the clinical signs or in the arterial oxygen concentration.
They found that thymol was well absorbed from the gut, reaching peak levels between five and seven hours after being given. Prof. van den Hoven points out that there were not enough horses in the trial to come to firm conclusions about the rate of absorption and excretion of thymol in the horse. But the results suggest that twice daily dosing should be adequate to maintain detectable blood levels for 24 hours.
The researchers conclude that the improvement in lung function was due essentially to the action of the active components of the herbal preparation. They suggest that further research is warranted into the use of the product in clinical situations.
For more details see: Study of the effect of Bronchipret on the lung function of five Austrian saddle horses suffering recurrent airway obstruction (heaves) R Van den Hoven, H Zappe, K Zitterl-Eglseer, M Jugl, C Franz. Veterinary Record (2003) 152, 555 - 557