Inhibition by Some Allelochemicals of Intake of Individual Meals by Meadow Voles1

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Abstract
A large number of allelochemicals may occur in forage plants but only a few of them can be studied in detail with large animals. Therefore, studies with small animals are essential to provide information that may be common to many animals or contribute towards the justification of further research with large animals. The objective of these experiments was to determine the relative importance of allelochemicals that are common in forages as they affect feed intake by the meadow vole (Microtus pennsylvanicus). The allelochemicals were fed alone or together in single meals to meadow voles. Gramine, hordenine sulfate, and tryptamine‐HCl, which occur in reed canarygrass (Phalaris arundinacea L.) were diluted to various concentrations with potato starch. Crownvetch (Coronilla varia L.) plants were grown with adequate or limiting levels of N and irradiation to the lowermost leaves to provide plants with different levels of β nitropropionic acid (NPA). Semisynthetic diets with various levels of NPA or combinations of NPA with one of the alkaloids were prepared by mixing the test chemicals with potato starch.Intakes of semisynthetic diets by the voles were inhibited by each of the allelochemicals. Inhibition by gramine and tryptamine were similar and greater than the inhibition with hordenine when measured on a weight basis. Inhibition by the three alkaloids was similar on a molecular basis. The intake of fresh leaves of crownvetch was probably limited by NPA and some additional inhibitor(s). The inhibitory effect of the alkaloids on intake was additive when they were fed in mixtures in synthetic diets. A synergistic effect on intake was obtained with diets that contained mixtures of gramine and NPA. We conclude that the biological activity of hordenine is of sufficient magnitude to warrant further work to determine its prevalence‐in the field and effects on animals.