The Value to Herbivores of Plant Physical and Chemical Diversity in Time and Space

Abstract

Whether foraging on pastures or rangelands, herbivores encounter plant species that differ in their concentrations of nutrients. They also all contain various secondary compounds that at too high doses can be toxic, but at the appropriate dose many of these toxins may have medicinal benefits. The quantity of forage an animal consumes depends on the other forages it selects because nutrients and toxins interact. Food intake also depends on an individual's morphology and physiology, and marked variation is common, even among closely related animals, in needs for nutrients and abilities to cope with toxins. Thus, individuals can better meet their needs when offered a variety of foods that differ in nutrients and toxins than when constrained to a single food. Nonetheless, we have focused on a few species, often grown in monoculture, and we have reduced concentrations of secondary compounds with little appreciation for their roles in protecting plants against herbivores, pathogens, and competitors. In nature, where diversity of plants is the rule and not the exception, eating a variety of foods is how animals cope with, and may benefit from, secondary compounds. The potential benefits of creating mixtures of plant species whose nutrient and secondary compound profiles complement one another are obvious, though much remains to be learned about how to reconstruct agro‐ecosystems with plants that complement and enhance one another structurally, functionally, and biochemically.

In vitroindications for favourable non-additive effects on ruminal methane mitigation between high-phenolic and high-quality forages

“…This could be explained by the attempt to achieve a better nutrient balance, to find the optimum medicinal benefit and to minimise the harmful effects of each of the toxins (13,37,38,40) .…”

Feeding behaviour of sheep fed lucerne v. grass hays with controlled post-ingestive consequences

“…This motivation for diversity may be explained by the 'satiety hypothesis' (Provenza et al, 2007;Villalba et al, 2009a and2009b), which suggests that animals acquired transient aversions for a food just eaten as a result of sensory input and post-ingestive feedbacks (nutrients and toxins) interacting along concentration gradients. This transient change in food palatability caused animal to search for a different food and then to eat a diverse diet.…”

Precision livestock production: tools and concepts

“…Persistence of aversions can be enhanced by providing alternative forages, particularly when the alternatives are complementary to the basal diet (Kimball et al, 2002). Finally, ruminants have a greater susceptibility to form long-term preferences and aversions when they are young (Launchbaugh et al, 2001), and they are able to regulate intake of chemicals that ameliorate the deleterious effects of plant toxins (Provenza et al, 2007, Villalba et al, 2006. Thus, animals can be "trained" to avoid perfectly safe foods and to increase their preference of plants that are not naturally preferred (Villalba & Provenza, 2000b).…”