Tannins in Ruminant Nutrition: From Obstacle to Opportunity
The adverse effects of tannins are often discussed, and there are valid reasons for this. These compounds have the ability to bind to proteins, precipitating them and reducing their digestibility or even making them indigestible.
At times, they also interfere with the digestion of valuable carbohydrates, such as starch, by encapsulating its granules. We have previously discussed this in past articles when describing the characteristics of sorghum grain.
However, tannins also have a positive side that can offer numerous benefits when used appropriately.
| The right tannins, in the appropriate doses, can improve protein utilization in the rumen and help reduce greenhouse gas (GHG) emissions. How? In the following pages, we will explain the mechanism of action of tannins and provide practical tips for their optimal use. |
WHAT ARE TANNINS?
These compounds are a type of polyphenols, characterized by having multiple hydroxyl (-OH) groups in their structure.
There are two main categories of tannins:
Hydrolyzable tannins: Derived from gallic acid, a phenolic compound that appears as a white or yellowish crystalline solid. These tannins break down in the body under certain conditions, such as the acidic environment of the abomasum. Additionally, they have antioxidant properties.
They are found in various plants, with tea, horse chestnut, and certain fruits being their most common sources (see Figure 1).
Figure 1: Structure of gallic acid, the fundamental molecule in the composition of hydrolyzable tannins.
Condensed tannins: Also known as proanthocyanidins, these are flavonoid oligomers that are not easily broken down in the body. These tannins are characterized by their astringent taste, which creates a dry and rough sensation in the mouth when consuming foods or drinks that contain them, such as wine, tea, and certain fruits (see figure 2).
Figure 2: Example of the structure of condensed tannins.
Additionally, they are attributed with beneficial properties for animal health, such as antioxidant and anti-inflammatory effects. However, in excess, they can interfere with the absorption of certain nutrients.
BENEFITS OF TANNINS FOR RUMINANTS
| The inclusion of tannins in ruminant diets, at appropriate concentrations, can offer significant benefits for their health and performance. |
Figure 3: Trees and plants that produce tannins used in animal feed. 1: Red willow; 2: Lotus corniculatus; 3: Chestnut; 4: Acacia Mearnsii
These polyphenolic compounds have the ability to bind to proteins, slowing their degradation in the rumen and allowing a greater amount of protein to reach the small intestine intact. This increases the availability of essential amino acids, improving nitrogen utilization.
This ability can be particularly beneficial in diets with excess degradable protein, such as those based on high-quality pastures (Orlandi et al., 2015).
| A study by Min et al. (2003) analyzed the impact of concentrated tannins in forages intended for ruminants. The positive impact of tannins on protein digestion has been demonstrated with low concentrations (20-45 g of condensed tannins/kg of dry matter). |
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» However, when the concentration of condensed tannins exceeds 55 g/kg of dry matter, voluntary intake and nutrient digestibility can be compromised, leading to an adverse effect on production. The decrease in intake can be attributed to lower food palatability caused by the astringent taste of the tannins.
Since not all ruminants are sensitive to astringency, other theories have also been developed that link the reduction in intake to factors more related to the potential adverse effects of excessive tannins on digestion.
» In this regard, it is possible that alterations in the ruminal microbiota lead to a slowing down of fermentation, causing feelings of satiety, or that animals develop aversions and rejection towards tannins (Frutos et al., 2004), triggered by digestive discomfort experienced in previous encounters with high-tannin foods (Salem et al., 2009).
| They are powerful antioxidants, neutralizing free radicals and preventing lipid peroxidation (Fraga del Corral et al., 2021). In low doses, tannins have the ability to modulate the ruminal microbiota, as we will see later. Additionally, it has been shown that tannins have antiparasitic effects, being effective against common internal parasites in sheep, such as Haemonchus contortus, and in cattle, such as Ostertagia ostertagi and Cooperia oncophora (Hoste et al., 2006; Naumann et al., 2017). This further highlights their usefulness in the health management of ruminants. |
Finally, some studies suggest that tannins could extend the shelf life of meat products from supplemented animals by improving oxidative stability and reducing meat discoloration (Luciano et al., 2009; Jenko et al., 2018).
Although it is necessary to determine if all tannins present the same effectiveness and what the optimal dose would be, it has been shown that these compounds can improve the health properties of meat, influencing its fatty acid composition and increasing its protein content (Jenko et al., 2018).
Figure 4: Tannins that have already been extracted, as they are used for addition to diets
LTANNINS AS REDUCERS OF GREENHOUSE GAS EMISSIONS (GHGs)
The inclusion of tannins in ruminant diets offers significant potential to promote sustainability in animal production by reducing greenhouse gas emissions.
This approach has sparked growing interest in scientific research in recent years, as effective solutions based on natural products or specific foods are sought to minimize the environmental impact of livestock farming.
| Min and Solaiman (2018) reported linear reductions in methane (CH₄) production in goats and sheep as the concentration of tannins in their diets increased. This finding was supported by several literature reviews (Cardozo-Gutiérrez et al., 2021) and recent meta-analyses (Scholz et al., 2023). |
These studies report that numerous in vitro and in vivo results support the idea that increasing the level of condensed tannins leads to a reduction in ruminal CH₄ concentrations and an increase in the molar proportions of propionate, butyrate, and total volatile fatty acids.
| Fonseca et al. (2023) observed that, although some studies suggest that condensed tannins are more effective at reducing methane production, hydrolyzable tannins tend to be more easily degraded in the rumen, which can lead to less predictable effects on methane production. |
| Given the property of tannins to reduce protein degradation, the consumption of tannin-rich foods (Eugène et al., 2021) or the addition of tannins to diets (Pozo et al., 2022; Batelli et al., 2024) results in a change in nitrogen excretion. More dietary protein passes into the small intestine, and less NH₃ is absorbed through the ruminal wall. |
This translates into a higher proportion of unused nitrogen being eliminated through feces rather than excreted through urine. Since fecal nitrogen is more stable, the release of ammonia (NH₃) and nitrous oxide (N₂O) into the atmosphere is reduced. Therefore, it is generally considered that a greater elimination of nitrogen through feces is favorable for the environment.
To achieve positive effects on greenhouse gas emissions without reducing production, the administered tannin dose is crucial. A low dose may not have significant effects, while a dose that is too high may have anti-nutritional effects, as we mentioned earlier, reducing feed intake and digestibility.
 However, higher doses resulted in a decrease in feed intake and milk protein production, highlighting the need for an appropriate balance in the use of tannins in ruminant diets to maximize their environmental and nutritional benefits. |
There is much research ahead, but these results suggest that condensed tannins can be an effective natural alternative to mitigate the environmental impact of ruminant production systems.
However, caution is also needed!!
Tannins can be beneficial for ruminant health, but their inclusion in the diet must be handled with care to avoid negative effects. As mentioned, in addition to interfering with the digestion and absorption of valuable nutrients like proteins and carbohydrates, they can also hinder the utilization of other nutrients.
| Condensed tannins can bind to minerals such as aluminum, calcium, copper, iron, and zinc, which can reduce their bioavailability (Naumann et al., 2017). |
| Excessive consumption can cause gastrointestinal irritation, manifesting as diarrhea, colic, and dry mouth. In severe cases, excessive intake of tannins has been associated with liver and kidney toxicity (Mbatha et al., 2002). |
IN SUMMARY
| Tannins are compounds that, when present in adequate amounts, can offer a range of benefits for ruminants, while simultaneously reducing the greenhouse gas emissions (GHGs) they produce. They improve the animal’s health and immune status, control parasites, modulate the microbiota, and increase protein utilization, ultimately boosting production and even animal products. |
| If we add to this the characteristic of being products directly extracted from nature, we believe that tannins can play an increasingly important role in achieving more efficient and sustainable feeding systems. Research on tannin sources and their optimal doses is essential to optimize their use and transform these compounds into allies for ruminant nutrition. |
Read the original article in Spanish at nutriNews LATAM.
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