Self-medication and homeostatic behaviour in herbivores: learning about the benefits of nature’s pharmacy

Abstract

Traditional production systems have viewed animals as homogeneous 'machines' whose nutritional and medicinal needs must be provided in a prescribed manner. This view arose from the lack of belief in the wisdom of the body to meet its physiological needs. Is it possible for herbivores to select diets that meet their needs for nutrients and to write their own prescriptions? Our research suggests it is. Herbivores adapt to the variability of the external environment and to their changing internal needs not only by generating homeostatic physiological responses, but also by operating in the external environment. Under this view, food selection is interpreted as the quest for substances in the external environment that provide homeostatic utility to the internal environment. Most natural landscapes are diverse mixes of plant species that are literally nutrition centres and pharmacies with vast arrays of primary (nutrient) and secondary (pharmaceutical) compounds vital in the nutrition and health of plants and herbivores. Plant-derived alkaloids, terpenes, sesquiterpene lactones and phenolics can benefit herbivores by, for instance, combating internal parasites, controlling populations of fungi and bacteria, and enhancing nutrition. Regrettably, the simplification of agricultural systems to accommodate inexpensive, rapid livestock production, coupled with a view of secondary compounds as toxins, has resulted in selecting for a biochemical balance in forages favouring primary (mainly energy) and nearly eliminating secondary compounds. There is a global need to create a more sustainable agriculture, with less dependence on external finite resources, such as fossil fuels and their environmentally detrimental derivatives. Self-medication has the potential to facilitate the design of sustainable grazing systems to improve the quality of land as well as the health and welfare of animals. Understanding foraging as the dynamic quest to achieve homeostasis will lead to implementing management programs where herbivores have access not only to diverse and nutritious foods but also to arrays of medicinal plants.

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

“…Nutrients shaping the intensity of costs and benefits during self-medication PSC are not consumed in a vacuum, they are ingested with other chemicals during a meal which in turn interact with the herbivore's physiological processes, feeding patterns and prior experiences with foods (40,41) . All these interactions can modify the potential benefits and penalties that different chemicals impinge on herbivores.…”

Forty research issues for the redesign of animal production systems in the 21st century

“…The appropriation and inclusion of learning processes and related empirical skills into management practices (I6) is entirely relevant to an agroecological approach. One focus will be animal ability to self-medicate in rangeland-based systems for which clear-cut evidence is still missing (Villalba and Provenza, 2007;Gradé et al, 2009). Inter-specific differences could be analyzed according to the 'fight and flight' theory against nematode infections, in which the two strategies regulating gastrointestinal infection (immune response v. behavior) are not mutually exclusive (Hoste et al, 2010).…”

The nature of nutrition: a unifying framework

“…Examples of the latter include refractory fibre (e.g. lignin from plants and chitin from some animal foods), and a range of secondary metabolites that play various roles from toxic defences to essential antioxidants and even antibiotic components that act as medicines (Huffman 2001(Huffman , 2003Villalba and Provenza 2007).…”

“…Self-medication, or zoopharmacognosy (Rodriguez and Wrangham 1993), is the phenomenon in which animals use plant secondary metabolites or other non-nutritional substances to prevent or treat disease (Huffman 2003;Villalba and Provenza 2007). Although much remains to be done in this field (Lozano 1998;Hutchings et al 2003), research shows that poisoned or parasitised animals can specifically select foods containing nonnutrient compounds that help them to recover.…”