An investigation into the use of garlic supplements in horses in the United Kingdom

Introduction: It has been suggested that garlic is one of the most commonly fed herbal supplements used in the equine industry. Garlic bulbs contain a complex mixture of organosulfer compounds. Allicin has been cited as the most biologically active compound of garlic, responsible for the majority of its therapeutic effects (Rahman, 2006). Allicin is not present in raw garlic; however, when the bulb is crushed, alliin is rapidly converted to allicin by the enzyme alliinase. Research suggests that the allicin content of garlic varies according to the preparation it is given in, indicating that the effect of garlic may vary according to the form it is given in (Rahman, 2006). Furthermore, certain preparations of garlic, such as freeze-dried garlic, have been linked to side effects such as Heinz body anaemia (Pearson et al, 2005). However, there is limited equine focused research in this area, and no current recommendations regarding safe dosage. Therefore, further research is needed to establish guidelines for its use, to minimise the risk of side effects in horses.
Material & Methods: An online questionnaire was posted in UK regional horse related groups on Facebook. This was used to obtain information on most common preparation of garlic, most common reason for using garlic and whether respondents were aware of side effects associated with its use. Descriptive statistics were calculated and Chi-Squared test for independence was used to compare nominal data. Kruskal Wallis testing was used for ordinal and nominal data. Results were considered statistically significant when p<0.05.
Results: Responses from 359 owners/ caretakers were put forward for data analysis. Garlic was used by 39% of respondents. The majority of respondents fed garlic all year around (53%), whilst 38% said they only fed garlic during summer months (April-September). The most common reason for using garlic was as a fly repellent (44%). Other reasons included boosting the immune system (15%), and respiratory health (12%). The most common preparations of garlic used were granules (57%) and powder (35%). Participants were asked to include the dosage of garlic used, however responses varied in their units of measurements, e.g. ‘1 scoop’, ‘’a small sprinkle’ ‘25g’. Furthermore, many participants could not remember how much they fed. This made quantities difficult to compare and analyse. Most participants (96%) were not aware of any side effects associated with garlic use in horses. However, 14% were aware that anaemia has been linked to garlic supplements.
Discussion & Conclusion: This is the first study to identify the prevalence of garlic use in horses. Overall findings of this research indicated that garlic is widely used amongst equestrians. There is some evidence to support garlic’s use as a fly repellent in humans (Valerio and Maroli, 2005). However, more rigorous equine specific research in this area is necessary. Garlic granules and garlic powder were the most widely used preparations of garlic, but the potential impact of garlic preparation requires further investigation due to the possible impact of differing levels of allicin. Although the majority of respondents were unaware of any side effects caused by garlic, 14% did identify anaemia as a side effect as reported by Pearson et al. (2005). Further research is therefore warranted to make recommendations regarding safe levels of garlic intake in horses.