The chemistry of pasture: secondary metabolites and ruminant nutrition
Studying secondary metabolites in tropical forages made me see that forage plants hold potential well beyond supplying protein, energy and fibre.
Translated from the Portuguese original, which is the version the author wrote. Read it in Portuguese.
When a farmer picks a forage for the herd, certain numbers tend to come first: dry matter yield, protein, fibre and digestibility. They matter, but there is another part to the story. Beyond nutrients, plants carry compounds able to act on the rumen environment and on the way the animal makes use of the diet.
These are the secondary metabolites, a group that includes tannins, saponins, flavonoids, terpenes and alkaloids. In the plant they take part mainly in defence and adaptation. In ruminant nutrition, what draws attention to them is their capacity to interact with the microorganisms of the rumen.
And to speak of the rumen microbiota is to speak directly of nutrition. Bacteria, fungi, protozoa and archaea take part in the fermentation of feed and allow cattle to make use of components they could not digest on their own. So when a substance in the diet changes the rumen microbiota, it may also change how well the nutrients are used.
One example comes from a crop well known on Brazilian farms: sugarcane. Recent research has been looking at polyphenol-rich cane extracts in ruminant feeding. In a study published in 2026 with lactating Holstein cows, supplementation shifted the rumen microbiota and showed a tendency towards higher short-chain fatty acids and propionate. Other work with lambs also found changes in the microbiota and a reduction in methane production. The results, however, vary with dose, diet and animal category.
The interest in these compounds does not lie in wiping out the rumen microorganisms, but in modulating fermentation — favouring particular populations and metabolic routes, and cutting back processes that represent losses of nutrients and energy.
This also comes close to an important discussion in animal production: the rational use of antimicrobials and bacterial resistance. Some plant metabolites show antimicrobial activity and are being studied as part of nutritional strategies to modulate microbial populations. There is still a great deal to understand before such results become practical recommendations.
In the end, it may be worth looking at a forage beyond protein, fibre and tonnes per hectare. There is chemistry going on inside these plants — and understanding how it talks to the microorganisms of the rumen may open new paths towards more efficient livestock farming.
References
MARINO, E. D. et al. Effects of sugarcane-derived polyphenol supplementation on ruminal fermentation, methane emission, and microbiome in Holstein cows. Frontiers in Animal Science, v. 6, art. 1739442, 2026. DOI: 10.3389/fanim.2025.1739442
PRATHAP, P. et al. Effects of sugarcane-derived polyphenol supplementation on methane production and rumen microbial diversity of second-cross lambs. Animals, v. 14, n. 6, art. 905, 2024. DOI: 10.3390/ani14060905