Sheep foraging behavior in response to interactions among alkaloids, tannins and saponins

Abstract

BACKGROUND: A mixture of plant species adds biochemical diversity to pastures that may enhance productivity while decreasing reliance on herbicides and insecticides. All plants contain secondary metabolites (PSMs) that interact in plant communities in a variety of ways. Our objective was to determine if PSM diversity enhanced food intake when sheep were allowed to select from foods that varied in concentrations of tannins, saponins, and alkaloids. We hypothesized that intake of foods containing alkaloids would increase when sheep were offered supplemental foods with tannins and saponins. The alkaloid gramine is proteinaceous in nature, tannins bind to proteins in the gut, which enhances excretion of proteins, so we hypothesized tannins would bind to gramine and enhance its excretion from the body. The alkaloid ergotamine is steroidal, saponins have a high affinity for binding to lipid and steroidal compounds in the gut and then being excreted, so we hypothesized saponins would bind to ergotamine and enhance its excretion from the body.

Phytochemical complementarities among endophyte-infected tall fescue, reed canarygrass, birdsfoot trefoil and alfalfa affect cattle foraging

“…Sheep also eat more when offered foods that contain terpenes, tannins and oxalates than when offered foods with only one or two of these SC (Villalba et al, 2004). Sheep fed either gramine or ergotamine in combination with tannin-or saponin-containing foods had higher intakes of food than sheep offered only foods with gramine or ergotamine (Lyman et al, 2008). All of these findings are consistent with the hypothesis that SC can complement one another to increase herbivore's intake of 'unpalatable' plant species, with the potential to better maintain the nutrition and health of animals and biodiverse landscapes (Provenza, 2008;Provenza and Villalba, 2010).…”

“…Although the varieties of RCG we studied did not differ in concentrations of NDF, N or alkaloids, cattle that first grazed the 'highalkaloid' variety of RCG spent more scans (%) eating ALF than cattle that first grazed the 'low-alkaloid' variety of RCG (33% v. 23%; Figure 4). Although RCG contains alkaloids such as gramine, which in too high concentrations reduce forage intake, all commercially available varieties of RCG have been selected for low concentrations of alkaloids that do not adversely affect forage intake (Marten, 1972;Lyman et al, 2008). Although the concentration of gramine we measured in our samples did not differ between the two varieties of RCG used in this study, other alkaloids not measured could have accounted for the different foraging responses observed between the two varieties.…”

Preference by sheep for endophyte-infected tall fescue grown adjacent to or at a distance from alfalfa

“…However, temporal changes in preference -even when in the aforementioned range -are indicative of the impact of nutrients and toxins on food selection by herbivores (Villalba et al, 2002b). This is relevant in situations, like in this study, when differences in the nutrient profile of food alternatives were small or when the concentration of ergovaline in the forage was below toxic levels (Lyman et al, 2008;Bernard et al, 2013). Changes in preference suggest lambs in our study were able to discriminate between the two fescue types assayed and traded-off the concentration of nutrients and plant secondary compounds across time.…”

“…Given pre-loads of energy (in starch) or nitrogen (in casein), lambs subsequently prefer flavors previously paired with nitrogen or energy, respectively, during the ensuing meals (Villalba and Provenza, 1999). Lambs ingesting diets deficient in Ca and P also acquire preferences for supplements that provide these minerals (Villalba et al, 2008). Thus, sheep select balanced diets, and in the process, they recognize different internal states and associate the flavors of different foods with their post-ingestive effects (Provenza, 1996).…”

Intake pattern and nutrient supply of lactating sheep selecting dried forage from woody plants and straw offered in binary or multiple choice

“…An increasing plant species diversity of the diet gives the animals the opportunity to compose their own mixed diet (Duncan et al, 2003). This enables the animal to consume more plants either complementary in nutrient composition, or with potentially harmful compounds (Lyman et al, 2008) by benefitting from the biochemical complementarity of these compounds (Manteca et al, 2008). Generally, a more diverse feed offer could increase intake (Rogosic et al, 2008) by increasing the animals' motivation to eat (Ginane et al, 2002) and improve performance by giving the animals the chance to select a nutritionally optimised diet (Duncan et al, 2003).…”