The study of tannins, their applications, and benefits to animals is advancing vigorously, opening horizons that encompass everything from nutritional strategies to the concept of "one health." To better understand them, it is important to be aware of the evolutionary history of ruminants and tannins, which have formed a positive co-evolutionary relationship to this day.
Tannins, also called polyphenols, are secondary compounds found naturally in some plants such as grapes, sorghum, chestnut trees, persimmons, and oak, and are known for their strong astringent taste. They are produced as a defense mechanism against predators to prevent the predation of unripe fruits and other parts of the plant. Thus, 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.
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Classification of tannins
The advancement in 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 non-soluble 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 livestock farming, demonstrating improved feed efficiency and growth performance in poultry and beef cattle (in various zootechnical species).
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Desirable aspects in the use of tannins
As mentioned above, tannins have an effect against certain microorganisms, which can be an important tool for rumen manipulation, seeking to optimize rumen functions and, subsequently, maximize zootechnical performance.
Research shows that tannins have an important effect against gram-positive bacteria such as Streptococcus bovis, an important lactic acid bacterium responsible for abruptly lowering ruminal pH, leading animals to ruminal acidosis. This action occurs mainly with the use of hydrolyzable tannins, which after the hydrolysis process can release ellagic or gallic acid, both with antibacterial action.
Additionally, tannins are also known for their ease of complexation with proteins and carbohydrates, reducing digestion in the rumen and making them available for subsequent digestion and absorption by the animal. This characteristic can be an important tool for nutritionists aiming for a greater passage of true protein from the rumen to the intestine. This reduction in protein digestibility in the rumen also reduces the amount of ammonia (NH3), which, at high levels in the rumen, becomes particularly harmful to reproduction. Furthermore, it increases the energy expenditure in the process of metabolizing the molecule into urea and its subsequent reuse and excretion via urine.
Finally, but no less importantly, a vast amount of research addresses the use of tannins as one of the main strategies for mitigating enteric methane (CH4) emissions. However, this mitigating action is not fully elucidated, but it is known that within the group of microorganisms inhibited by tannins, there are numerous methanogens, such as archaebacteria, cellulolytic bacteria, and protozoa.
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BIBLIOGRAPHY CONSULTED
FYHRQUIST, P. et al. Antimycobacterial activity of ellagitannin and ellagic acid derive 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, [SL], 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, [SL], v. 30, no. 12, p. 3875-3883, Jan. 1991. Elsevier BV. http://dx.doi.org/10.1016/0031-9422(91)83426-l.
