In vitro and in vivo effects of Acacia mearnsii De Wild extract for cyathostomin control in horses.
Authors: Silva G L S, Curcio U A, Boufleur J A, Borges D G L, Nakatani M T M, Freitas M G, Borges F A, Faria F J C, Silva R H P, Franco G L
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Acacia mearnsii Extract for Cyathostomin Control in Horses Anthelmintic resistance in equine cyathostomins has prompted investigation into plant-based alternatives, with condensed tannins showing promise in laboratory settings. Silva and colleagues evaluated an Acacia mearnsii (black wattle) extract across both in vitro and in vivo models, using 30 naturally infected Pantaneiro horses across two farms over 28 days, with fecal egg count reduction testing (FECRT), egg hatchability assays, and haematological monitoring at baseline and conclusion. The extract demonstrated meaningful in vitro efficacy, with EC50 values of 13.2 mg/mL (Farm A) and 14.9 mg/mL (Farm B), and significantly reduced egg hatchability in laboratory conditions; however, the in vivo results proved disappointing, with no statistically significant difference in fecal egg counts between treated (3.18% reduction) and control groups (3.09% reduction) after 28 days. Blood parameters and body condition remained unchanged across both groups, suggesting the extract neither harmed nor benefited the horses systemically. Whilst condensed tannins merit continued investigation for parasite control, this disconnect between laboratory efficacy and field performance highlights the critical importance of in vivo validation before adopting botanical extracts into clinical practice—the dosage, bioavailability, or rumen metabolism of the extract may have limited its antiparasitic effect in the living horse, despite promising in vitro results.
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Practical Takeaways
- •Despite promising in vitro results, Acacia mearnsii extract at 25 g daily failed to reduce parasite burden in naturally infected horses and cannot be recommended as an alternative to conventional anthelmintics
- •The discrepancy between in vitro efficacy and in vivo failure suggests bioavailability or dosage issues that would need to be addressed before reconsidering this extract for field use
- •Continue to rely on conventional anthelmintic protocols while monitoring for resistance; consider alternative parasite management strategies such as pasture rotation and targeted selective treatment
Key Findings
- •Acacia mearnsii extract showed in vitro efficacy with EC50 values of 13.2-14.9 mg/mL and reduced egg hatchability
- •In vivo fecal egg count reduction test (FECRT) showed no significant difference between treated and control groups (3.18% vs 3.09%, P > 0.05)
- •No differences in blood hematological or biochemical parameters between treatment and control groups after 28 days
- •Tannin extract efficacy observed in vitro did not translate to clinical efficacy in naturally infected horses