It was hypothesized that a tannin-rich legume such as sainfoin attenuates the negative postingestive effects of ergot alkaloids in tall fescue. Thirty-two 4-mo-old lambs were individually penned and randomly assigned to a 2 × 2 factorial arrangement with 2 legume species, sainfoin (SAN; 2.9% condensed tannins) or cicer milkvetch (CIC; without tannins) and a mixed ration containing tall fescue seed (50:30:20 seed:beet pulp:alfalfa) with 2 levels of endophyte infection (endophyte-infected tall fescue seed [E+; 3,150 ug/L ergovaline] or endophyte-free tall fescue seed [E-]). For a 10-d baseline period, half of the lambs were fed SAN and half were fed CIC and all lambs had ad libitum amounts of E-. In an ensuing 10-d experimental period, the protocol was the same except half of the lambs fed SAN or CIC received E+ instead of E-. Subsequently, all lambs could choose between their respective legume and seed-containing ration and between E+ and E-. Finally, an in vitro radial diffusion assay was conducted to determine whether tannins isolated from SAN would bind to alkaloids isolated from E+. All groups consumed similar amounts of E- during baseline period ( > 0.10), but lambs ate more E- than E+ during the experimental period ( < 0.05) and lambs offered SAN ate more E+ than lambs offered CIC ( < 0.05). Groups fed E- during the baseline and experimental periods had similar rectal temperatures ( > 0.10), but lambs fed E+ had lower rectal temperatures per gram of feed ingested when supplemented with SAN than with CIC ( < 0.05). Lambs fed E+ had greater concentrations of hemoglobin and more red blood cells than lambs fed E- ( < 0.05), but plasmatic concentrations of cortisol and prolactin did not differ among treatments ( > 0.10). All lambs preferred their treatment ration over their treatment legume, but lambs in the SAN and E+ treatment ate more legume + ration than lambs in the CIC and E+ (CIC-E+; < 0.05) treatment. All lambs preferred E- over E+, but lambs in the CIC-E+ treatment ate the least amount of E+ ( < 0.05). Binding of isolated SAN tannins to protein was reduced by the E+ isolate ( < 0.05), suggesting a tannin-alkaloid complexation but only from tannins extracted from SAN fed early in the experimental period. In summary, SAN supplementation increased intake of and preference for E+ and reduced rectal temperatures relative to CIC supplementation. Our results suggest that these effects were mediated by the condensed tannins in SAN through alkaloid inactivation, an interaction that declined with plant maturity.

Medusahead (Taeniatherum caput-medusae (L.) Nevski) is one of the most detrimental invasive annual grasses impacting the sustainability and function of rangeland in the western United States. The annual grass possesses high concentrations of tissue silicon (Si) that may facilitate invasion through key plant characteristics such as increased plant fitness, structure, and anti-nutritive qualities. These characteristics may affect known invasion processes such as increased plant productivity, slow litter decomposition, and decreased herbivory facilitating a positive feedback cycle of invasion. However, Si is not considered an essential element and is often overlooked as a factor of medusahead invasion. Thus, this article provides a synthesis of plant Si, medusahead, and the self-reinforcing feedback cycle of invasion. We also discuss how current control strategies address plant characteristics determined by Si, and finally suggest numerous research avenues that may aid in novel or improved control strategies that target the medusahead-silica relationship.

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Herbivores satiate on single foods ingested too frequently or in excess. We hypothesized that exposure to the same unpalatable food too frequently or in excess causes satiety, which in turn would reduce subsequent use and preference for this food when alternatives become available. In each of three experiments, twenty-four lambs were randomly assigned to three treatment groups (8 lambs/group), where they received high (Ad libitum), intermediate (100-200 g/d) or low exposure (20-40 g/d) to three unpalatable foods: The invasive weed medusahead (Experiment 1), an alfalfa:quebracho tannin ration (70:30; QT) (Experiment 2), or wheat straw (Experiment 3). After exposure, all groups in Experiments 1 and 3 received a simultaneous offer of the unpalatable food and a novel food that changed across four consecutive preference tests: Grape pomace (Test 1), barley straw (Test 2), tall fescue hay (Test 3), and beet pulp (Test 4). Lambs in Experiment 2 received a simultaneous offer of each of these novel foods and the same novel food containing 30% quebracho tannins. During exposure, lambs in Experiment 1 showed a low and cyclic pattern of medusahead intake, and the group with intermediate level of medusahead exposure showed greater intake values than the Ad libitum group, followed by the group with the lowest level of exposure (P < 0.05). For the rest of the experiments, intake was Ad libitum > intermediate > low level of exposure (P < 0.05). During preference tests, lambs with the least level of exposure to the unpalatable foods tended to consume more medusahead (35% to 37%; P = 0.11) or wheat straw (15 to 30%; P = 0.10) than lambs that received greater levels of exposure. In contrast, differential exposure to QT did not influence subsequent preference for tannin-containing foods (P = 0.33), but animals with the greatest level of exposure to QT consumed 24% more alternatives (i.e., non-tannin containing foods) than lambs that had received the lowest level of QT exposure (P < 0.05). Intake of alternative novel foods during preference tests increased with increments in nutritional quality from grape pomace and barley straw to tall fescue hay and beet pulp (P < 0.05), suggesting that lambs discriminated the nutritional value of the novel foods. In conclusion, repeated exposure to unpalatable foods has the potential to further reduce their utilization when alternatives-even when novel-become available. This effect appeared to be influenced by the chemical characteristics of the unpalatable food and it has implications for the coexistence of plant species in grazed communities.