Phytochemicals in animal health: Diet selection and trade-offs between costs and benefits

Summary

This narrative review examines the dual role of plant secondary compounds (PSC) as both defensive toxins and medicinal agents in grazing livestock diets. The authors synthesise evidence that sheep and goats self-select for condensed tannin-rich forage when parasitised, demonstrating parasitism-triggered self-medication that improves health. The paper highlights that understanding the net benefit of such behaviour requires moving beyond simple cost–benefit analysis to account for nutrient–PSC interactions, social influences, and feeding patterns—insights applicable to development of improved grazing management strategies.

Regional applicability

The findings are relevant to United Kingdom pastoral farming, particularly for organic and grass-fed systems managing parasitism in sheep and goats without synthetic anthelmintics. The review's emphasis on self-selection of medicinal plants in diverse pasture environments aligns with UK grazing practices and regenerative farming interests, though specific applicability would benefit from UK-based validation studies.

Key measures

Preference for condensed tannin-containing foods; parasite burden; health outcomes; cost–benefit analysis of phytochemical ingestion; nutrient–phytochemical interactions

Outcomes reported

The paper reviews evidence that sheep and goats self-medicate by increasing preference for condensed tannin-containing plants when parasitised, and explores how phytochemical–nutrient interactions and feeding context influence the net cost–benefit calculus of this behaviour for animal health and welfare.

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