Tannins as an alternative growth promoter in monogastric species

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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.

Plant Source

Monogastric species

Concentration in diet

Effects on Monogastric

Sweet chestnut

wood extract

Chicken

0.07% and 0.2%

Antinutritive effects not observed.

Chestnut (Castanea

Swine

1%, 2% and 3%

Increase in the intestinal villi height, mucosal thickness and villus perimeter; reduced large intestinal apoptosis and mitosis, no negative impact on liver.

Tannic acid

Chicken

1% Tannic acid depending on

climatic conditions

Better quality of fatty acid composition  in breast muscle of broilers.

Chestnut

Chickens specifically in layers

0.20%

Reduce cholesterol content and increase monounsaturated fatty acid content of eggs.

Chestnut tannin

Extract (Castanea

sativa Miller)

Chickens specifically in layers

2 g/kg

Increase unsaturated fatty acids; significantly decreased in cholesterol in eggs

High-tannin red

sorghum

Chickens

(broilers)

16 g/kg

Retention of calcium, Utilisation of phosphorus and nitrogen in body.

Chestnut

Pigs

0%, 5%, 10% and 15%

Reduction in digestibility of dry matter, crude protein, ether extract,

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.

Components

Medicinal Uses

Pine needles and dry oak leaves

Control of coccidian infection

Extract of chestnut shell

Enteritidis, Clostridium perfringens, Staphylococcus aureus, and Campylobacter jejuni.

Sweet chestnut extracts

Reduction of Salmonella infection, Escherichia coli, Bacillus subtilis, Salmonella enteric serovar Enteritidis

Gall nuts

Treatment of diarrhea and dermatitis

Acacia Nilotica

Antimutagenic and cytotoxic effect.

Quebracho Tannins

Reduction of worm eggs counts and inhibition of development of nematodes and lungworms

Chestnut extracts

Control of Clostridium perfringens

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).

Source

Concentrations of tannin in diet

Animal/Bird

Effect

Chestnut

0.71–1.5%

Pigs

Reduced feed efficiency; No effect on feed intake, body weight gain and carcass traits

Chestnut

0.16–0.19%

Pigs

Increase growth rate.

Chestnut

1–3%

Pigs

Optimize intestinal absorption through increasing small intestinal villi height, perimeter and mucosal thickness.

Chestnut

0.15% to 1.2%

Broiler

Reduced pathogenic bacteria (Clostridium perfringens) and parasite (Eimeria maxima, Eimeria tenella

and Eimeria acervulina)  in the gut.

Chestnut tannin

250, 500 and

1000 mg/kg

Chicken

Reduce number of E. coli and coliform bacteria in small intestine. Increases number of Lactobacillus.

Grape pomace

5–10%

Broiler

Increased oxidative stability of meat by increasing polyunsaturated fatty acids content of meat. Increased commensal bacteria (Lactobacillus) and decreased the counts of clostridium.

Grape pomace

2.80%

Pig

Reduce absorption of mycotoxins in the

gastrointestinal tract.

Tannic acid

1%

Broiler

Improved fatty acid profile of breast muscle.

Chestnut

0.25-0.5%

Layer

Reduce cholesterol content of eggs.

Chestnut

0.45% and 0.5%

Rabbit

Increase feed intake and live weight gain.

Purple loosestrife

0.2%, 0.4% and

0.3%

Rabbit

Trigger immune system by increasing total white blood cell count.

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. 

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