Selenium plays an important role in poultry diets and participates in a variety of functions. A large number of studies in laying hens have proven that compared to inorganic selenium, yeast selenium has better biological utilization and can improve egg production performance and egg quality. The improvement of the performance of laying hens by yeast selenium is mainly related to its effective participation in the body's antioxidant system, improvement of the body's immunity and improvement of fallopian tube health. This article combines the research on selenium in laying hens in recent years and reviews its functions.

Keywords: yeast selenium, egg production performance, egg quality, antioxidant, immunity, fallopian tube

Selenium was first discovered by the Swedish chemist Berzelius in 1817 , but it was not until the 1950s that French scientists first discovered that selenium has a protective effect on the liver. Over the past few decades, a great deal of research has been conducted on selenium. In poultry, selenium mainly participates in proteins in the form of selenomethionine to form selenoproteins. Another part enters the body as selenocysteine ??and participates in body protein composition, playing a wide range of roles. There are more than 100 selenoproteins known so far, which play important roles in the body.

The application effect of organic selenium in laying hens

There are currently two main sources of selenium commonly used in poultry diets, namely inorganic selenium and organic selenium. Inorganic selenium mainly includes Sodium selenate and sodium selenite, organic selenium is mainly yeast selenium, etc. A large number of studies have found that adding organic selenium to the diet of laying hens can improve the production performance and egg quality of laying hens. Yang Yu et al. (2018) found that adding selenium yeast (Sela Selenium, Alltech) to the diet of aging laying hens can significantly increase the egg production rate and reduce the feed-to-egg ratio after 8 weeks (Table 1). Among them, adding 0.2ppm yeast selenium can increase the egg production rate by 8.3% and improve the feed-to-egg ratio by 5.2%. On the 14th day of the experiment, it was observed that adding yeast selenium can significantly increase the protein height and increase the Hastelloy unit (Figure 1), indicating that yeast selenium can improve the freshness of eggs and thereby extend the shelf life. In addition to improving the internal quality, the use of yeast selenium can also significantly improve the eggshell strength on the 42nd day of the test and effectively enrich it in the yolk (Figure 2). The role of selenium in yeast in improving production performance and egg quality is inseparable from the following functions.

Table 1: Effect of adding selenium yeast to the diet on the production performance of laying hens in the late laying period

Figure 1: Effect of adding selenium yeast to the diet on the quality of 14-day-old eggs

Figure 2: Adding yeast selenium to the diet affects 42-day eggshell thickness

Yeast selenium improves the body’s antioxidant capacity

Conditions for large-scale breeding of modern animal husbandry Under such conditions, we inevitably face various stresses, such as density stress, heat stress, group stress, oxidative stress, etc. Stress often causes an increase in free radicals in the body. Improving antioxidant capacity can effectively remove them from the body. Excess free radicals, reducing stress damage. The body's antioxidant system mainly includes two categories, the enzymatic system and the non-enzymatic system. The non-enzymatic system includes glutathione, VC, VE and other antioxidant substances, while the enzymatic system includes catalase (CAT). ), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), etc. Among them, GSH-Px is one of the important enzyme system components. One of the essential components is selenium. Selenium deficiency will cause Resulting in a decrease in GSH-Px activity. Yang Yu et al. (2018) studied that adding selenium yeast to the diet of laying hens can improve the antioxidant capacity of plasma and liver. Among them, GSH-Px activity, total antioxidant capacity (T-AOC) and T-SOD activity in plasma were all increased. Significantly increased, while malondialdehyde (MDA) content significantly decreased, and GSH-Px activity in the liver was significantly increased (Table 2). Further, it was found through PCR that adding yeast selenium can significantly increase the expression of GSH-Px1 and thioredoxin reductase (Trxr1) in the liver (Figure 3), which are involved in the glutoxidation protein and thioredoxin systems respectively. , thereby playing the role of antioxidant, scavenging free radicals and inhibiting cell apoptosis.

Table 2: Effect of adding selenium yeast to the diet on antioxidant indicators of laying hens

Figure 3: Adding different levels of selenium yeast to the diet of laying hens on liver GSH- Effect of relative expression of Px1 and Trxr1mRNA

Yeast selenium improves immunity

In addition to participating in the antioxidant function of the body, selenoproteins also play an important role in the immune system .

Leng et al. (2003) conducted a 7-week trial using 220 1-day-old Isa brown laying hens, mainly comparing the effects of yeast selenium and inorganic selenium on the development of the immune system of laying hens during the brooding period. The results showed that adding yeast selenium at the same level (0.2ppm) can significantly increase the deposition of selenium in the heart, lungs, gizzard, spleen and kidneys, and the deposition amount further increased as the amount of yeast selenium added increased. Further comparison of the levels of related immune cells in the duodenum, bursa of Fabricius and cecal tonsils showed that compared with inorganic selenium, adding yeast selenium could significantly increase the number of duodenal CD3+ cells in the first week and improve the number in the fourth week. Trends in CD4+ cells in the peribursal bursa and CD8+ cells in the duodenum at week 7 (Fig. 4). The development of the immune system of laying hens mainly occurs in the first 6 weeks. The establishment of the immune system in the early stage will help the body resist the invasion of various pathogenic bacteria and reduce the occurrence of diseases. Better autoimmunity during the laying period also means better nutrients are available for egg deposition. Ensuring the health of the chickens can ensure overall production performance.

Figure 4: Effect of adding yeast and selenium to the diet of laying hens on immune cells