The study of tannins, their applications, and their benefits to animals is advancing vigorously, opening horizons that involve nutritional strategies and the concept of one health. To better understand them, it is important to be aware of the evolutionary history of ruminants and tannins, which formed a positive co-evolutionary relationship up to the present day.
Tannins, also called polyphenols, are secondary compounds found naturally in some plants such as grapes, sorghum, Portuguese chestnut trees, persimmons, and oak, and are known for their astringent taste. They are produced as a defense mechanism against predators to avoid the predation of immature fruits and other parts of the plant. Therefore, ruminants, long before their domestication, came into contact with this substance in their daily search for food by consuming fruits, tree bark, and leaves rich in tannins, providing a variety of health benefits to the animal.
Also read: What are hydrolyzable tannins – HTs?
The discovery of these compounds has allowed us to classify them as hydrolyzable and condensed tannins. Hydrolyzable tannins are water-soluble polyphenols that can be broken down into smaller molecules (ellagic or gallic acid and glucose) and are known for their antimicrobial, antioxidant, and anti-inflammatory properties. Condensed tannins are insoluble polyphenols formed by the condensation of flavan-3-ols and are known for their antimicrobial, antiviral, and antifungal properties. Their popularity lies in the fact that these compounds present themselves as a natural alternative to antibiotics – mainly ionophores, widely used in cattle breeding, demonstrating improvements in feed efficiency and growth performance in birds and beef cattle (in various livestock species).
As mentioned above, tannins have an action against certain microorganisms, which can be an important tool for ruminal manipulation, seeking to optimize ruminal functions and maximize zootechnical performance.
Research has shown that tannins have an important action against gram-positive bacteria such as Streptococcus bovis, an important lactic acid bacteria responsible for lowering ruminal pH abruptly, leading animals to ruminal acidosis. This action is mainly due to the use of hydrolyzable tannins, which after the hydrolysis process can release ellagic or gallic acid, both with antibacterial action.
Tannins are also known for their ease of complexation with proteins and carbohydrates, reducing digestion in the rumen environment and making it available for subsequent digestion and absorption by the animal. Such a characteristic can be a tool for nutritionists aiming for greater passage of true protein from the rumen to the intestine. This reduction in protein digestibility in the rumen environment also reduces the amount of ammonia (NH3), which, at high levels in the rumen, becomes harmful, especially to reproduction. In addition, it increases energy expenditure in the metabolism process of the molecule into urea and subsequent reuse and excretion via urine.
Last, but not least important, a vast amount of research addresses the use of tannins as one of the main strategies for mitigating enteric methane (CH4) emissions. The mitigating action is incompletely elucidated, but it is known that within the group of microorganisms inhibited by tannins, there are numerous methanogens, such as archaeobacteria, cellulolytic bacteria, and protozoa.
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REFERENCES CONSULTED
FYHRQUIST, P. et al. Antimycobacterial activity of ellagitannin and ellagic acid derivate rich crude extracts and fractions of five selected species of Terminalia used for treatment of infectious diseases in African traditional medicine. South African Journal Of Botany, [S.L.], v. 90, p. 1-16, jan. 2014. Elsevier BV. http://dx.doi.org/10.1016/j.sajb.2013.08.018.
SCALBERT, Augustin. Antimicrobial properties of tannins. Phytochemistry, [S.L.], v. 30, n. 12, p. 3875-3883, jan. 1991. Elsevier BV. http://dx.doi.org/10.1016/0031-9422(91)83426-l.
