Quercetin is one of the most widely distributed natural flavonoid compounds in nature, existing abundantly in various fruits, vegetables, grains, and some traditional Chinese medicinal materials. Quercetin possesses various biological activities such as antibacterial, anti-inflammatory, antioxidant, and anti-obesity effects, making it a highly valuable research and practical application candidate as a nutritional supplement and food additive in modern antibiotic-free livestock and poultry farming. According to reports, quercetin is beneficial in enhancing the production performance of livestock and poultry, improving the quality of meat and eggs; strengthening the immune system of livestock and poultry, effectively preventing and treating diseases; improving the utilization rate of nutrients, and regulating the metabolism of livestock and poultry bodies.

1. Enhancing the production performance of livestock and poultry, and improving the quality of meat and eggs

Research has found that adding an appropriate amount of quercetin to the diet of Hy-Line Brown laying hens can significantly reduce the average feed-to-egg ratio, the rate of cracked and soft-shelled eggs, and the phosphorus content in eggshells. It also significantly improves the average egg-laying rate, relative eggshell weight, eggshell strength, eggshell thickness, and calcium content in eggshells, indicating that quercetin can enhance the feed conversion efficiency of Hy-Line Brown laying hens and improve the quality of eggs, thereby increasing economic benefits. Another study showed that adding quercetin to the diet of laying hens can also significantly increase the Haugh unit, egg yolk phospholipid, and crude protein content, while significantly reducing egg yolk cholesterol content.

During road transportation, pigs are often subjected to various stressors such as noise, fasting, overcrowding, and temperature fluctuations, which can easily lead to stress and damage to intestinal barrier function. The impact of transportation stress on the gastrointestinal tract is profound, and quercetin has been found to alleviate the damage to the intestine caused by transportation stress. Through experimental studies on the effects of adding quercetin on intestinal integrity, intestinal ROS levels, and intestinal inflammation in pigs under transportation stress, it was discovered that quercetin has a protective effect on intestinal integrity. Specifically, adding 25 mg/kg of quercetin to the diet of finishing pigs significantly increased the height of small intestinal villi and the mRNA levels of occludin and zonula occludens-1 (ZO-1). Quercetin also reduced serum levels of LPS, ROS, and malondialdehyde, as well as reduced serum levels of TNF-α, interleukin-1 (IL-1), IL-6, and monocyte chemoattractant protein-1β (MCP-1β). These findings indicate that quercetin can improve pork quality and enhance disease resistance in finishing pigs.

Research has shown that adding an appropriate amount of quercetin to the diet of broiler chickens can improve the brightness and redness of meat, as well as enhance the stability of meat quality by reducing the rate of fat oxidation and extending the shelf life of meat. Adding quercetin to the diet can also reduce the content of oxidized cholesterol in lamb meat. Furthermore, it has been found that adding quercetin to the diet of lambs can decrease the proportion of saturated fatty acids in lamb meat and reduce lipid peroxidation. The results of studies on the effects of quercetin on livestock and poultry meat quality indicate that adding quercetin to the diets of livestock and poultry can improve meat quality by inhibiting lipid peroxidation through its antioxidant properties, thereby enhancing the stability of meat quality and extending its shelf life.

Quercetin possesses the ability to protect the liver and reduce lipid accumulation in the liver, effectively mitigating the occurrence of fatty liver. Experimental studies have found that quercetin has a positive impact on cow health, particularly during the stressful period of early lactation, where it can alleviate metabolic disorders such as fatty liver and ketosis acidosis in cows. The supplementation of quercetin significantly reduces the activity of plasma transaminases and glutamate dehydrogenase in postpartum cows, indicating that quercetin can alleviate liver damage in cows.

2.Enhancing the immune capacity of livestock and poultry, regulating gut microbiota, and effectively preventing and controlling livestock and poultry diseases

Livestock and poultry diseases are the primary causes of mortality and reduced farming efficiency. Quercetin, with its diverse biological activities such as immune enhancement and gut microbiota balance regulation, has been proven by many scholars to effectively boost the immune capacity of livestock and poultry and modulate the intestinal flora, thereby reducing the incidence of diseases in these animals.

Studies have found that quercetin can significantly increase the spleen index, thymus index, and serum levels of immunoglobulin A (IgA), immunoglobulin M (IgM), complement C3, complement C4, IL-4, and TNF-α in AA broilers. It can also significantly increase the mRNA expression of TNF-α, TNF receptor-associated factor-2 (TRAF-2), TNF receptor superfamily member 1B (TNFRSF1B), nuclear factor-κB p65 subunit (NF-κBp65), and interferon-γ (IFN-γ), while significantly reducing the mRNA expression of NF-κB inhibitor α (IκB-α). These findings suggest that quercetin mediates the immune response through the TNF-α-triggered NF-κB signaling pathway, thereby improving the immune function of broilers and enhancing their disease resistance.

Quercetin can also mitigate intestinal damage in pigs during transportation by regulating the expression of the NF-κB signaling pathway. There is a close relationship between gut microbiota and the host in terms of energy metabolism and material exchange. Gut microbiota and the host can exchange substances through degradation and synthesis. Lysed cells and extracellular enzymes can be utilized by microorganisms, while the host can also utilize enzymes, vitamins, stimulants, and microbial cell components produced by microorganisms. Normal gut microbiota can directly participate in physiological and biochemical activities within the intestine, assisting the host in degrading food and providing various nutrients, including vitamins, amino acids, and simple carbohydrates. Additionally, normal gut microbiota exhibit biological antagonism and immune effects against exogenous and opportunistic pathogens, significantly enhancing the host's mucosal anti-infective capabilities. Studies have shown that quercetin can reduce the number of Pseudomonas aeruginosa, Helicobacter pylori, Salmonella, Staphylococcus aureus, Escherichia coli, Clostridium perfringens, and Campylobacter jejuni in the cecum of AA broilers while increasing the number of Bifidobacterium. Similarly, in Hy-Line brown chickens, quercetin reduces the number of Escherichia coli, Staphylococcus aureus, Salmonella, Pseudomonas aeruginosa, Streptococcus faecalis, and Enterococcus in the cecum while increasing the numbers of Bifidobacterium and Lactobacillus. These findings suggest that quercetin promotes the growth of beneficial bacteria such as Lactobacillus and Bifidobacterium, which can prevent the colonization of harmful bacteria through competitive exclusion and produce active substances to inhibit the growth of harmful bacteria like Clostridium perfringens and Escherichia coli, thereby protecting the host from infections caused by harmful bacteria and exogenous pathogens, and reducing the occurrence of host diseases.

3.Enhancing Nutrient Utilization and Regulating Metabolism in Livestock and Poultry

Low protein utilization efficiency has been a major challenge in livestock and poultry production. Recent research on quercetin has indicated its potential to improve this situation. Studies on AA broilers have shown that the addition of quercetin to the diet can enhance protein deposition and improve protein utilization efficiency in feed by enhancing gastrointestinal enzyme activity and activating the mechanistic target of rapamycin (mTOR) signaling pathway. Quercetin can also promote protein utilization by intestinal epithelial cells in pigs by regulating the expression of amino acid transporters, small peptide transporters, and the mTOR signaling pathway.

Furthermore, quercetin regulates metabolism in livestock and poultry, helping to lower blood glucose and lipid levels. Research has found that quercetin can improve lipid metabolism in AA broilers by reducing blood lipid content, increasing the secretion of leptin and adiponectin, and activating the PI3K/PKB signaling pathway, ultimately leading to decreased abdominal fat deposition. Additionally, quercetin can reduce triglyceride content in broiler hepatocytes by promoting lipid breakdown regulated by the peroxisome proliferator-activated receptor alpha (PPARα) signaling pathway, thereby decreasing lipid deposition in broilers.

Research has revealed that quercetin can mitigate the adverse effects of streptozotocin-induced oxidative stress by enhancing antioxidant enzyme activity, reducing malondialdehyde and nitric oxide levels, and activating the expression of genes related to the PI3K/PKB signaling pathway, which regulates glucose metabolism and alleviates oxidative damage. This results in decreased fasting blood glucose and insulin levels, indicating that quercetin inhibits streptozotocin-induced hyperglycemia in AA broilers, likely through reducing oxidative stress. Studies have also shown that while the addition of quercetin to the diet does not significantly affect blood lipid levels in egg-laying hens during peak production, it can significantly increase the serum levels of very low-density lipoprotein cholesterol, apolipoprotein B, and apolipoprotein A, thereby enhancing the total phospholipid and lecithin content in egg yolks. Furthermore, research suggests that quercetin promotes the conversion of cholesterol to bile acids, facilitating the excretion of cholesterol from the body.

Against the backdrop of the comprehensive ban on antibiotics, quercetin, as a novel green additive, holds vast potential for application in livestock and poultry production. However, in practical applications, quercetin still faces numerous limitations. For instance, the manufacturing process is not yet mature, and its price remains relatively high compared to antibiotics, hindering its widespread market availability. Although its biological activities have been thoroughly studied, the underlying mechanisms of action still require further in-depth research. Additionally, the optimal dosage of quercetin in feed remains to be determined. Therefore, to accelerate the progress of quercetin as an alternative to antibiotics, numerous researchers must continue to intensify their efforts in quercetin-related research, aiming to bring it to the market as soon as possible.

References

[1] Xiao Fenglin. Research Progress on Quercetin as an Antibiotic Substitute [J]. Feed Review, 2021(01): 7-10.

[2] Fei Jinbo. Application of Quercetin as a Feed Additive in Livestock and Poultry [J]. New Agriculture, 2022(16): 62-63.

[3] Xia Yingying, Zou Tiande, Li Shuo, et al. Nutritional and Physiological Functions of Quercetin and Its Prospects for Feed Application [J]. Chinese Journal of Animal Nutrition, 2021, 33(02): 729-736.

About the Author

Xiaonisha, a food technology professional holding a Master's degree in Food Science, is currently employed at a prominent domestic pharmaceutical research and development company. Her primary focus lies in the development and research of nutritional foods, where she contributes her expertise and passion to create innovative products.