The potential of selected plant secondary components to control parasites in horses; a nutritionist perspective

Definitions

Plant secondary metabolites (PSM) form a complex group of biochemicals made by plants that are regarded as being not directly essential to the life of the plant. Currently, at least five classes of secondary metabolites (glucosinolates, benzoxazinoids, terpenes, aromatics, and green-leaf volatiles) are confirmed to act in the natural defence system aiding plants to protect themself e.g. from herbivory (Erb and Kliebenstein, 2020; Mueller-Harvey, 2006).

Tannins are polyphenolic PSM’s that crosslink with proteins and as such they can nutritionally exert both beneficial and detrimental effects. Cross linkages between tannins and dietary proteins can affect dietary protein utilisation. Tannins can crosslink with the resident gastro-intestinal microbiota, hence, modulating the microbiome and redirecting the fermentation and metabolites thereof. Tannins can improved animal welfare and health through the prevention of bloat and lowering intestinal parasite burdens. Tannins can be categorised into two groups, the hydrolysable and condensed tannins.

Hydrolysable tannins are produced by a wide variety of plants and can be divided into gallotannins, ellagitannins and complex tannins. They can be easily hydrolysed within an acidic or alkali environment, or in hot water and/ or by enzymes.

Condensed tannins, also referred to as proanthocyanidins, are polyphenolic compounds of high molecular weight that mainly consist of oligomers or polymers of flavan-3-ol monomers (e.g. catechin, epicatechin). Depending on the chemical structure of the monomeric unit, they are classified into four groups, the two most dominant groups being the procyanidins (PC) and prodelphinidins (PD).

Key Take Home Messages

Hydrolysable and condensed tannins both show anthelmintic effects in monogastric and polygastric animal species. Studies show that tannins can give a decrease in larvael exsheathment and faecal egg count, but results are varying in success rate.

Tannin efficacy against parasites depends amongst others on its molecular structure. In addition, the site where the parasites resides and develop within the gastro intestinal tract and the environmental conditions, are factors that could influence efficacy.

Feeding tannins containing legumes either as a fresh forage or as a silage or haylage potentially could be a strategy to reduce gastro-intestinal parasite burden in horse and to decrease the use of anthelmintics.

Applying tannin extracts as a therapeutic dietary additive could be another alternative strategy to aid in gastro-intestinal parasite control in horse.

References

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Further reading

• Baert, N., Pellikaan, W. F., Karonen, M., and Salminen, J-P., 2016. A study of the structure-activity relationship of oligomeric ellagitannins on ruminal fermentation in vitro. Journal of Dairy Science, 99, 10, 8041–8052. http://dx.doi.org/10.3168/jds.2016-11069
• Hatew, B., Hayot Carbonero, C., Stringano, E., Sales, F., Smith, L., Mueller-Harvey, I., Hendriks, W. H., and Pellikaan, W. F., 2015. Diversity of condensed tannin structures affects rumen in vitro methane production in sainfoin (Onobrychis viciifolia) accessions. Grass Forage Science, 70, 474-490. http://dx.doi.org/10.1111/gfs.12125
• Huyen, N. T., Fryganas, C., Uittenbogaard, G., Mueller-Harvey, I., Verstegen, M. W. A., Hendriks, W. H., and Pellikaan, W. F., 2016. Structural features of condensed tannins affect in vitro ruminal methane production and fermentation characteristics. Journal of Agricultural Science, 154 (8), 1474- 1487. http://dx.doi:10.1017/S0021859616000393
• Verma, S., Taube, F., and Malisch, C. S., 2021. Examining the variables leading to apparent incongruity between antimethanogenic potential of tannins and their observed effects in ruminants - A review. Sustainability, 13, 5, 2743, https://doi.org/10.3390/su13052743