Is Tannin Good For Ruminants?

Tannin, also known as tannic acid, is a polyphenolic compound widely found in the veins of plants (Galla Chinensis, pomegranate peel, barley, sorghum, mung bean, onion, grape, tea). This yellow or brownish-yellow loose powder has strong hygroscopicity, gradually darkening in air, easily soluble in water, ethanol, acetone. According to its structural characteristics, it can be divided into hydrolyzed tannins (HT) and condensed tannins (CT).

Tannin has active chemical properties and is easy to combine with proteins, carbohydrates, heavy metal salts, vitamins and inorganic metal ions to form macromolecular complexes, which will reduce animal feed intake and the bioavailability of some nutrient elements, and has been considered as an anti-nutrient factor in feed. However, due to the special physiological and digestive characteristics of ruminants, the research results in recent years have shown that the appropriate amount of tannin added to the diet has the effects of protecting rumen protein, regulating intestinal flora, inhibiting harmful bacteria, anti-parasite and anti-oxidation.

Biological properties of tannins

Protein agglutination

The results showed that monomax combined with proteins to form macromolecular complexes, which coagulate and precipitate proteins into insoluble proteins, and enhance the physical and chemical stability of collagen fibers. The molecular weight of condensed tannins, the flexibility of their conformation, and their water solubility affect their ability to precipitate proteins. Similarly, a protein’s molecular mass, conformation stability, and number of amino acids can also affect its affinity for a particular condensed tannin.

Chelate metal ions

Phenolic substances can affect the resource availability or activity of metal ions through a chelating mode. The results showed that the tannins of plants contain several o-phenol hydroxyl groups that can be used as multigroup ligands, which can be combined with a central ion such as heavy metal ions (lead, copper, bismuth, mercury, etc.) and basic metal ions (calcium, barium, strontium, etc.) to form a ring complex, which can form salt and precipitate at different pH values. Tannin chelates are not available to organisms, and the metal’s REDOX potential is altered by metal ion chelators or prevented from participating in REDOX reactions. Therefore, metal ion chelators are often used as inhibitors or promoters of Fenton oxidation.


This phenol has strong reducibility and is a good antioxidant with its aromatic base phase pair stabilization. Biological antioxidants are generally divided into three types: enzymes (such as superoxide dismutase), group formation inhibitors (such as Fenton reaction inhibitors) and free radical eliminators (such as VE). The results showed that condensed tannins and hydrolyzed tannins with or without protein had stronger antioxidant capacity than small molecular phenols, and could eliminate various oxygen free radicals and reactive oxygen species. In vitro results show that many naturally occurring low molecular mass phenols have the same scavenging group capacity as antioxidants VA and VE. So tannins are natural antioxidants and free radical scavengers with real value.


Tannin itself has almost no toxicity, but when the proportion of high-tannin diets in ruminants is too high, the polymeric tannin can be degraded by microorganisms in the rumen environment of livestock, and a variety of phenolic compounds with lower molecular weight can be produced. Some of it is absorbed directly into the bloodstream through the rumen wall. Once the amount exceeds the body’s detoxification capacity, reaching the threshold concentration in the blood and body fluids, it will cause poisoning. The main manifestations are loss of appetite, cessation of rumination, hypothermia, constipation, edema and proteinuria.

Effects Of Tannin On Ruminants

Rumen protein protection

Tannins and proteins have a high affinity, their complex reduces the dissolution of proteins in the rumen, increases the amount of rumen proteins and avoids rapid degradation by rumen microorganisms, thus improving the utilization of proteins. When rumen pH was between 5 and 7, monobiod formed complexes with proteins in plant-based diets. When this tannin-protein complex enters the stomach (pH 2.5) and small intestine (pH 8-9), it is broken down by pepsin and trypsin to form small molecules that are easily absorbed, thus achieving the protective effect of rumen protein.

The results showed that the protein degradation rate decreased with the tannin content increasing. On the other hand, tannin can protect rumen protein by inhibiting the growth of rumen protein-breaking bacteria and reducing the number of some protein-breaking bacteria in the body. The degradation rate of dietary dry matter and in vitro gas production were significantly decreased, and the solubility of ammonia was significantly decreased by tannin. The concentration of condensed tannin was 0 and 1. 52 and 3.03 g/kg dry matter Onobrychis viciifolia (conglutinated tannin) were fed to cotton sheep. The results indicated that when the dietary conglutinated tannin of Onobrychis viciifolia was 3.03 g/kg, it could inhibit the activity of cellulose decomposing microorganisms in the rumen of sheep. It also enhanced the microbial activity of starch decomposition.

Nitrogen utilization and emission from feed

The tannin content of dry matter tea residue (tannin) was 0, 1.02, 2.04 and 3.06 g/kg. The results showed that tannin had no significant effect on fecal nitrogen excretion, but urine nitrogen excretion decreased linearly with tannin content increasing. The nitrogen retention rate increased linearly. The results showed that monobarb increased the utilization rate of feed nitrogen and reduced nitrogen discharge (Mueller-Harvey, 2006).

For meat Quality

Tannin had a strong inhibitory effect on some microorganisms related to fatty acid hydrogenation in the rumen. Lambing sheep were fed with Astragalus membranaceus, which was rich in tannin, as the only diet, and it was found that the content of linolenic acid (LNA) in intramuscular fat of lambs was increased by 4 times compared with the control group, and the ratio of docosaapentaenoic acid in long-chain fatty acids was higher than that in the control group (Priolo et al., 2005).

When Aspidosperma quebracho tannin was fed to sheep, it was found that prolonged refrigeration time could improve the stability of mutton color, and the addition of certain tannin in the diet could significantly reduce the content of methyl indole (skatole) in the intramuscular fat of lambs, as well as the smell of mutton (Priolo et al., 2009). These results indicate that monomax can effectively reduce the content of methyl indole in intramuscular fat of lambs.

For Milk Quality

Supplementation of 7.5% Tamarindus indica shells (containing condensed tannins) to the diets of high-yielding cows showed a significant increase in milk protein percentage, but no significant difference in milk yield and milk fat percentage (Bhatta et al., 2000). In vitro studies have shown that dietary supplementation with 7.5% (DM) of Acacia mearnsii tannin can affect the hydrogenation of rumen fatty acids and reduce the hydrogenation of linolenic acid by 20%. This is because the last step of rumen fatty acid hydrogenation is blocked by tannin. Namely, the conversion from 11-octadecanoic acid to stearic acid (SA) resulting in the accumulation of 11-octadecanoic acid (Khiaosa-Ard et al., 2009). However, some studies have shown that tannin has a positive effect on the deposition of 11-octadecanoenoic acid in the rumen.

Methane emission

During rumen metabolism of ruminants, 2% to 15% of the diet is discharged into the atmosphere in the form of methylane. Therefore, reducing the production of methylane can reduce the wave cost of feed energy and improve the efficiency of animal feed conversion. Some studies have shown that the addition of legume forage (containing tannin) to the diet reduces methane emission from ruminants. Replacing 1/3 of forage in the diet with tropical mimosa (high tannin content) was found to reduce methane emissions by 1/2 under in vitro culture conditions (Hess et al., 2003). Feeding goats with a tannic source of L. chinensis was found to reduce methane emissions at relatively low levels of condensed tannin in the diet without affecting overall intestinal digestibility of protein (Animut et al., 2008).