Plant secondary compounds abound in every plant mother nature has to offer. From common garden vegetables to poisonous plants, there are secondary compounds in every plant any animal, as well as we, chooses to eat. In the past, secondary compounds were mostly considered waste products of plant metabolism, but over the last several decades research has shown that these compounds play an active role in plant and animal behavior, health, and productivity. Though often seen only in terms of their negative impacts on intake and production, we are becoming increasingly aware of their beneficial roles in plant, animal, and human health. Providing herbivores with a diversity of plants to make up their diet allows them to regulate and mix foods so as to better utilize primary and secondary compounds, as well as enhancing economic and ecological performance.

The secondary compound gramine is an alkaloid found in reed canarygrass that is proteinaceous in nature. Endophyte-infected tall fescue contains the alkaloids perlolidine, perloline and ergotamine, which are all steroidal in nature. Tannins have a high affinity for binding proteins, and saponins are non-polar steroidal compounds with a high affinity for binding to lipids in the gastro-intestinal tract of animals. These findings suggest that animals ingesting foods with alkaloids may increase their preference for tannin or saponin-containing foods to reduce the negative impacts of these secondary compounds. Moreover, tannins and saponins hasten alkaloid excretion from the body, which might also allow animals to eat more high-alkaloid forages when presented with tannins first.

I tested the hypothesis that cattle and sheep foraging behavior is influenced by eating different combinations and sequences of forages containing secondary compounds. In pen and pasture trials, I showed that (1) sheep fed basal diets high in alkaloids (gramine or ergotamine) ate more when supplemented with food containing either tannins or saponins; (2) cattle that ate a 30-minute meal of tall fescue(alkaloid) subsequently preferred birdsfoot trefoil(tannin) to alfalfa (saponin), while cattle that first ate reed canarygrass(alkaloid) subsequently preferred alfalfa(saponin) to birdsfoot trefoil (tannin); and (3) cattle spent more time grazing tall fescue and reed canarygrass when they first ate birdsfoot trefoil (high in tannins) and alfalfa (high in saponins), respectively, than when they ate these forages in the reverse sequence.