Foraging in domestic herbivores: linking the internal and external milieux.

Abstract

Animals function and maintain well-being within the internal milieu through behavioural interactions with the external milieu. These interactions are complex. They involve an ongoing dynamics influenced by history, necessity and chance such that at any time an animal's foraging behaviour is a function: (i) of its evolutionary history, genetically expressed, in concert with its uniquely individualistic history of the social and biophysical environments where it was conceived and reared; (ii) of necessity due to its current nutritional, toxicological and medicinal state relative to the biochemical characteristics of foods it can potentially consume at any moment; and (iii) to chance occurrences that involve gene expression and environmental variability. This chapter discusses the various interactions and factors affecting the foraging behaviour of domestic herbivores, such as learning foraging behaviour by consequences, the need for homeostatic regulation, flavour-feedback associations and grazing behaviour regulation due to interaction of substances (nutrient-nutrient, toxin-toxin and nutrient-toxin interactions).

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

“…Evolution of foraging strategies that optimise nutrient intake (Belovsky, 1978;Stephens and Krebs, 1986) and fixed rules of thumb such as 'eat tall green grass' or 'avoid bitter' have also been proposed as mechanisms underlying diet selection in herbivores (Cassini, 1994). However, the 'sodium model of nutritional wisdom' is not a particularly good exemplar for energy, protein, minerals and vitamins because animals do not instinctively recognise through oduor/taste all of these nutrients, nor do they necessarily recognise all of the various configurations of any particular nutrient (Provenza and Balph, 1990;Provenza and Villalba, 2006). Beyond the evolution of fixed codes or static rules of thumb, animals evolved learning mechanisms to cope with the frequent changes occurring in the internal and external environment.…”

“…This monitoring-action loop is particularly relevant in living organisms because homeostasis is not static but inherently dynamic: set points, equilibrium states and biochemical processes change through time as organisms develop and preserve their integrity (Rose, 1998). Thus, feedback cycles do more than simply maintain variables within normal limits; they increase the flexibility and adaptability of a system's response Provenza and Villalba, 2006).…”

“…Thus, the receptor systems of the animal involves sensory receptors in the nose and mouth -that allow for food discrimination -and visceral receptors that respond to nutrients, toxins, osmosis and pressure, which inform the selector system of the animal (central nervous system) about the consequences of ingesting food (Figure 1) (Provenza, 1995 andProvenza and Villalba, 2006) Homeostatic behaviour can be observed in livestock fed diets that vary in nutrients. For instance, lambs and goats fed diets low in energy and protein prefer flavoured lowquality foods previously paired with intra-ruminal infusions of energy (starch, propionate, acetate) or nitrogen (urea, casein, gluten), respectively Provenza, 1996, 1997a, b andArsenos et al, 2000;Duncan and Young, 2002).…”

“…Our thesis is that food selection in herbivores can be interpreted as the constant quest for substances in the external environment that provide a homeostatic benefit to the internal environment (Provenza and Villalba, 2006). Under this view, nutrients, PSMs, medicines are all 'substances' with the same final utility: improving the welfare of cells and cellular processes that enable life.…”

“…We are just beginning to appreciate the importance of PSMs and biodiversity in the foraging behaviour of herbivores (Provenza and Villalba, 2006;Provenza et al, 2007). We believe creating mixtures of plants whose PSM profiles complement one another and allowing animals to selfmedicate using a diverse array of PSMs is the way to reduce the negative impacts of PSMs on animal production and to enhance animal health through the medicinal effects of PSMs.…”