Many warm-season perennial forage legumes produce biologically active plant secondary metabolites in the form of protein-precipitable polyphenols (proanthocyanidins). Proanthocyanidins may demonstrate biological activities in ruminants, including protein precipitation, antimicrobial activity, anthelmintic activity and enteric methane (CH₄) suppression. Proanthocyanidins are structurally diverse compounds, and those from some plant sources are bioactive, whereas those from others demonstrate almost no bioactivity in the ruminant.

Our primary objective is to conduct research that will provide new insights into the physiology of forage proanthocyanidins as it relates to plant-animal interactions. Primary interests include 1) Effect of abiotic and biotic stress on proanthocyanidin production, composition and biological activity, and 2) Identification of compositional characteristics of proanthocyanidins that influence biological activity.

Ongoing research involves an evaluation of the relationship between the composition of proanthocyanidins and protein-precipitating ability, as well as model development to predict rumen-bypass protein when ruminants consume forages containing proanthocyanidins. Ruminal-protein binding results in a shift in N excretion from urinary ammonia (NH₃-N) to fecal N, and increased amino acid flow to the small intestine, which results in greater amino acid absorption by the animal. We believe that proanthocyanidin composition may be an important factor in the non-linear relationship between dietary proanthocyanidins and rumen-bypass protein.

The elucidation of structure-function relationships of proanthocyanidins relative to enteric CH₄ suppression is ongoing. Interactions between rumen microorganisms and their ruminant host are mediated in part by chemical constituents of the host diet. Understanding how diet affects interactions between ruminants and gastrointestinal microbes could result in the use of novel forages to improve animal productivity and suppress ruminal CH₄, which could result in increased gross-energy intake by the animal. We speculate that the reduced substitution group and interflavan bond reactivity of some polyphenols leads to increased resistance to degradation and increased activity in the ruminant gastrointestinal tract, which could inhibit methane-producing microbes. Understanding the structure-activity relationships of proanthocyanidins will provide new insights into ruminant gastrointestinal microbial ecology.

We are evaluating the effect of maturity and growing season on forage quality and protein-precipitating ability of proanthocyanidins from tree species used by “browsing” ruminants in South Africa and North America. In semi-arid southern Africa, low herbaceous forage quantity, and even more so quality throughout the dry season are the most limiting factors in animal production. Browse from perennial trees can help fill this gap. However, widespread utilization of woody species requires more information regarding nutritional, digestive, and plant secondary characteristics. Our goal is to identify the best quality browse species so that we can maximize the use of novel forages as it relates to animal productivity and efficiency.

Understanding the physiological ecology of polyphenol-based plant secondary metabolites in plant-animal interactions and identifying key characteristics that influence biological activity will lead us closer to harnessing the potential of novel forages for use in improving overall animal performance and productivity.

Cooper, C.E., Naumann, H.D., Lambert, B.D., Muir, J.P., Kattes, D.H. Protein precipitable phenolic and nutrient concentrations in legumes respond differently to repeated defoliation and ontogeny. J. Plant Interact. Article In Press.

Naumann, H.D., Hagerman, A.E., Lambert, B.D., Muir, J.P., Tedeschi, L.O. and Kothmann, M.M. Molecular weight and protein-precipitating ability of condensed tannins from warm-season perennial legumes. J. Plant Interact. Article In Press.

Naumann, H.D., Armstrong, S.A., Lambert, B.D., Muir, J.P., Tedeschi, L.O. and Kothmann, M.M. 2014. Effect of molecular weight of condensed tannins from warm-season perennial legumes on in vitro larval migration inhibition of Haemonchus contortus. Vet. Parasitol. 199:93-98.

Naumann, H.D., Tedeschi, L.O., Muir, J.P., Lambert, B.D. and Kothmann, M.M. 2013. Effect of molecular weight of condensed tannins from warm-season perennial legumes on ruminal methane production in vitro. Biochem. Syst. Ecol. 50:154-162.

Muir, J.P., Lee, A.E., Lambert, B.D., Bow, J.R., Naumann, H.D., Reilly, J.L. 2013. Dry Matter, Carbon, and Nitrogen Yields of Four Great Plains Grasses with Forage and Bioenergy Potential. Crop Sci. 53:1799-1808.

Naumann, H.D., Muir, J.P., Lambert, B.D., Tedeschi, L.O. and Kothmann, M.M. 2013. Condensed tannins in the ruminant environment: A perspective on biological activity. J. Agric. Sci. 1 (1), 8-20.