Monogastric animal industry has witnessed an increase in feed prices due to several factors. This hike in prices of feed is mostly due to extreme competition over commonly used conventional ingredients. To restrain this trend, alternative ingredients of both plant and animal origin need to be sourced as well as growth promoters to be incorporated with feed.

In-feed antibiotics have been used over a period of time as growth promoters, which positively aids in feed conversion rates and consequently reduces the cost of production. However, it was discovered that the inclusion of the antibiotics could leave residue in meat/egg and its products, which consequently cause resistance to bacteria in humans. These multifaceted challenges compelled the researchers to find an alternative ingredient which can fill the gap. Tannins are considered to be the valid alternative antipathogenic molecule to the conventional feed ingredients which can be used as an alternative ingredient of antibiotics. Tannins are a group of polyphenolic compounds commonly found in the plant having antimicrobial, antiparasitic, antiviral, antioxidant, and anti-inflammatory properties. They are considered valuable in that they can replace antibiotics in monogastric animals feeds. Although the use of tannins in monogastric animal’ was discouraged over the years because of the antinutrient factors present in it. However, recent studies revealed that if tannins are used with watchfulness can be of benefit to monogastric animals.

The mechanism with which tannins promote growth in the monogastric animals are not as clear, however, it is suggested that the inclusion of tannins in low (appropriate) concentrations (Table 1) leads to an increase in feed intake, increased feed palatability, nutrient digestion and promoting the health status of the intestinal ecology.

Table 1: Dose of and nutritive effect of tannins in different monogastric farm animals

Mode of Action of Tannins and its Functions

Tannins are complex group of polyphenolic compounds having astringency properties present in a wide range of plant species. Tannins are the higher molecular weight proanthocyanidins with a molecular weight between 500 and 5000 Da. Acacia species belong to the family of Leguminosae in the plant kingdom, are considered the most common sources of tannins. However, these are also found in wood, bark, leaves and fruits. Tannins concentration in plant is dependent on the plant genotype, tissue developmental stage, and the environmental conditions.

Tannins have the ability to inhibit extracellular microbial enzymes. Therefore, tannins have been proposed as an alternative to antibiotics. Researchers suggest that tannins can be used in lieu of antibiotics, because bacteria such as Clostridium perfringens cannot develop resistance to them.

Applications of tannins for humans benefit apart from meat industry

Tannins have numerous applications for benefit of human. Some of the applications of tannins include their use as nutraceuticals to prevent cancer, cardiovascular disease, kidney disease, as well as diabetes. They are also used for tanning leather, wood adhesives and manufacturing ink. For medical purpose, tannins are use as antidiarrheal, a remedy for alkaloid and heavy-metals toxicity.  Tannin’s ability of to chelate heavy-metals, their antioxidant activity and antibacterial action are believed to be the mechanism of action to treat and prevent certain conditions such as diarrhea and gastritis in human. On the other hand, tannins inhibit extracellular microbial enzymes, deprivae the substrates required for microbial growth, or direct action on microbial metabolism through inhibition of oxidative phosphorylation.

In the laboratory, tannins are used as a reagent for experiments of detection of protein, alkaloids, and heavy metals due to their precipitating properties. In the beverage industry, tannins are used to clarify wine, beer, and fruit juices. Other industrial uses of tannins include as coagulants in rubber production and textile dyes.

Table 2. Medicinal uses of tannins.

Tannins on the productivity of monogastric animals:

Currently, most researchers have revealed that tannins originate from certain plant species can improve the intestinal micrflora enhancing gut health, and hence increase productive performance when applied appropriately in monogastric diets. However, adverse effects of high-tannin diets on monogastric animals’ performances have also been reported by many researchers. Therefore adequate concentrations of tannins are to be used to improved feed intake, health status, nutrition, and animal performance in monogastric farm animals (Table 3).

Table 3. Effects of tannins on health and productivity of monogastric animals.

In vitro studies have shown that tannins have antiviral, antibacterial and antitumor properties, however, a favorable outcome in the promotion of gut health was observed when used with other antimicrobials as growth-promoting factors such as probiotics. Therefore, natural extracts can be adopted as a valuable alternative to antibiotics in intensive animal farming. Poultry and swine nutrition are the most important sectors in which tannins have been used and Several commercial products are available containing tannins extracted from the European chestnut tree (Castanea sativa Mill.) and the American quebracho (Schinopsis spp.). Tannins from plant origin have been applied on intensive farms due to their ability to improve animal performance and health. The use of tannins in monogastric nutrition could have beneficial effects on the growth performances and gastrointestinal health status of both post-weaning and growing pigs. However, the effectiveness of tannin supplementation in weaned and finishers are highly related to the dose of administration, duration of supplementation and the presence of other sources of tannins in the basal diet in the feed regimen adopted.