Plant extract refers to a kind of substance with one or more biological functions derived from plants, which can improve the production performance of livestock and poultry, improve the quality of livestock products, enhance immunity, prevent some animal diseases and other functions.

Currently, plant extracts are widely used and come from a wide range of sources.

Most of these active substances are secondary metabolites in the growth and development of plants, and they are also the basis of biological functions as feed additives.

The chemical structure of their active components often includes groups such as phenols, ethers, terpenes, ketones, etc. These organic functional groups are not only the effectors for the identification and identification of active ingredients but also the binding sites for the factors related to target organs when they are acting in vivo.

Studies have shown that the application of plant extracts in animal diets has many biological functions, such as anti-oxidation, scavenging excess free radicals in the body, relieving oxidative stress, increasing the secretion of endogenous enzymes in the digestive tract, reducing the viscosity of chyme, increasing the utilization rate of nutrients and improving production performance.

Adding saponins, tannins and other plant extracts to a ruminant diet can also reduce the production of rumen methane and improve the utilization rate of nutrients.

Due to plant extracts in the composition and source of difference of effective components, the mechanism of its action also is not the same, different active ingredient within the animal body by multiple signaling pathways in target organs, in cell growth, proliferation, gene expression regulation and the activation of the complement system, immune enhancement, resisting oxidative stress, scavenging free radicals, anti-aging, inhibit the growth of malignant cells play a role in many aspects, such as, and then improve the production performance, enhance the immune response regulation and so on a variety of phenotypic traits.

Under the background of the current high attention to the safety of animal products and the sustainable development of animal husbandry, plant extract has been widely used in the feed of livestock and poultry, becoming a new type of antibiotic substitute due to its advantages of safety, efficiency, no residue, and no resistance.

There are many kinds of plant extracts used in production, mainly products extracted from different parts of plants or whole plants, and the content and function of the active ingredients vary according to the different parts used, harvesting seasons and producing areas.

At present, plant essential oil, polysaccharide, saponins, resveratrol, flavonoid compounds, plant tannins, and other ingredients are widely used.

Plant essential oil is a kind of aromatic oily liquid extracted from plant tissues and organs.

Essential oils can remove free radicals from the body, play an antioxidant role, and regulate the intestinal tract

The commonly used plant polysaccharides are a kind of compound polymerized by more than 10, usually hundreds or even thousands of monosaccharide molecules. As feed additives, they have many biological functions such as immune regulation, anti-tumor, and anti-aging, and have small toxic and side effects, and are not easy to cause residues in the animal body and products.

In chemical structure, saponins are high molecular weight glycosides, which are compounds formed by the combination of sugar and triterpene or steroidal glycoside ligands.

In traditional nutrition, saponins are often regarded as anti-nutrient factors, but later studies have shown that the addition of appropriate doses of saponins in the diet of ruminants or monogastric animals can play a variety of beneficial biological functions, including reducing the concentration of ammonia in the rumen of goats, increasing nitrogen utilization rate, inhibiting rumen parasites, and reducing methane production.

Studies have shown that resveratrol can increase the activity of antioxidant enzymes in animals, enhance the body’s antioxidant capacity, and at the same time can be healthy.

Flavonoids are a subclass of polyphenols, which can increase the turnover rate of proteins and have anti-inflammatory and antioxidant functions.

• Types and characteristics of common plant extracts

  Plant tannin, also known as plant polyphenols, is a kind of polyphenols compounds widely existing in plants.
  Tannins have long been considered anti-nutrients.
  The tannins in the feed will bind to the protein, thus reducing the degradation rate of the protein in the feed.
  With further research, the researchers found that tannins have dose-dependent biological effects, such as hemostasis, inhibition of microorganisms and anti-allergy at the appropriate dose.
  High concentration of concentrated tannins was found in red bean grass and thyme root. Studies have shown that a certain amount of red bean grass and thyme in diet can reduce the production of rumen methane.

• Main functions and mechanism of plant extracts

  With the deepening of research on plant extracts, various biological functions of plant extracts have been gradually recognized and applied in production, including growth promotion, anti-oxidation, antibacterial and anti-inflammatory, immune enhancement and methane emission inhibition.
  In addition, with the help of molecular biology and cell biology, relevant studies have been made on the molecular mechanism of plant extracts exerting apparent effects. However, due to the complexity of plant extracts composition and organism regulation, many mechanisms are still being explored.

Growth-promoting effect and its mechanism

Since Moore discovered in 1946 that streptomycin can promote the growth of broilers, antibiotics have been widely used as growth promoters in the breeding industry.
However, due to the use of antibiotics in feed, the drug residues in animals and products and the variation of pathogenic bacteria have aroused greater attention and sought.
Abdel-wareth found that adding 15 or 20g/kg of thyme and oregano to diets could significantly improve broiler chickens’ performance.
Cho studied the effects of thyme essential oil and star anise essential oil on the production performance of broilers infected with clostridium perfringens and found that 250mg/kg of the above plant extracts could significantly reduce the production performance

The growth-promoting mechanism of plant extracts may include the following aspects:

First, improve feed palatability to increase animal feed intake.

Clouard has shown that adding sweet orange extract (0.003 125% content) to the diets of weaned piglets can significantly improve the palatability of feed, increase the edible quality of feed, and increase feed intake of piglets.

Second, plant extracts can improve the secretion and activity of endogenous enzymes, improve intestinal microbial flora, and improve the utilization rate of feed nutrients.

Williams and other research has shown that adding a certain amount of fodder rate was plant essential oil can promote the secretion of endogenous enzymes such as amylase rates, improve the activity of digestive enzymes in the gut, so as to change the shape of the feed in the gut, for example, in turn, can reduce chyme viscosity increase of nutrients in feed digestibility, increase the absorption of nutrients;
Meanwhile, plant extracts can also improve intestinal microflora. Studies have shown that adding plant essential oils to diets can reduce the number of clostridium capsulatum in the intestinal tract and promote the colonization of beneficial bacteria such as lactobacillus and bifidobacterium.

Thirdly, it affects the conversion and utilization of nutrients in the body after absorption and improves the energy used for growth conversion.

Bravo added 100g/t mixture of plant extracts containing 5% carvacrol, 3% cinnamaldehyde and 2% capsaicin to the corn-soybean meal diet, which can significantly increase the body weight of broil chickens, improve feed utilization, increase carcass energy residence and reduce heat loss.

Fourth, regulate the secretion of growth-related hormones and promote the improvement of animal production performance.

Ariza-nieto found that adding 0.01% additives containing thymol and cinnamaldehyde (18%) in the diet of weaned piglets can significantly increase the content of igf-1 in plasma of weaned piglets, and at the same time, the body weight gain of weaned piglets also significantly increases, and the production performance is improved.

• Oxidation resistance and its mechanism

Current research suggests that the oxidative system and antioxidant system in the body and in normal circumstances, these two systems are in dynamic equilibrium, when due to the outside world or its own factors cause oxidation system cannot free radicals and their toxic metabolic products, will generate oxidative stress, oxidative stress can produce adverse effect to the body.

All the polyphenols in plants have antioxidant effects. Studies have proved that the extracts of various fruits, vegetables, and forage crops contain different kinds and amounts of polyphenols.

There are many kinds of polyphenolic compounds, including hydroxybenzoic acid, hydroxycinnamic acid, anthocyanins, lignans, flavonols, flavones and so on.

Such additives can enhance the antioxidant capacity of the body by enhancing the activity of antioxidant enzymes such as glutathione peroxidase and superoxide dismutase, so as to alleviate oxidative stress.

Lahucky found that adding 60mL oregano extract to pig diet can improve the antioxidant capacity of muscle, and when adding 10mL extracts from bee flower, oregano or sage to the diet, it can effectively improve the lipid and color stability of unprocessed pork.

Placha studied the effect of thyme essential oil on antioxidant performance of broiler chickens and found that adding 0.5g/kg thyme essential oil in diet can reduce MDA content in duodenal mucosa and kidney, and improve the integrity of intestinal function.

It has also been reported that artemisia annua powder contains a large amount of polyphenols and other compounds, and adding 2% or 4% dry artemisia annua powder to the diet of broiler chickens can significantly reduce MDA levels in chest and leg muscles.