Bile acid power: erecting a defensive shield for the liver

Foreword

With the continuous large-scale and intensive development of modern poultry industry, the number of laying hens in China has rapidly increased, thanks to the increase of oil in feed. Oil is the most commonly used energy source in layer feed. The addition of oil has played a variety of positive effects, such as improving egg production performance, egg quality, palatability, feed intake, animal immunity and reducing incidence rate. Meanwhile, the liver of laying hens is the main organ for lipid metabolism, with over 70% of fat synthesized in the liver. Excessive lipid accumulation in the liver can lead to severe metabolic disorders. Frequent stress and long-term use of fats in intensive farming can easily lead to Fatty liver hemorrhagic syndrome (FLHS) in laying hens during the late stage of egg production. FLHS is one of the main metabolic diseases in laying hens, which can cause severe damage such as liver fragmentation and fragility, liver bleeding and swelling, and liver color changing from dark red to earthy yellow or yellow brown. It can lead to low production performance and even increased mortality rate. FLHS has a huge economic impact on the poultry industry. Therefore, regulating lipid metabolism is crucial for maintaining health, improving egg quality traits, and preventing diseases.

Liver tissue morphology

As shown in Figure 1, with the increase of bile acid addition (200, 300, and 500 mg/kg), the number of fatty degeneration lesions decreased, and the white circular vacuoles in the cytoplasm of liver cells gradually decreased and became smaller. The number of fat droplets decreased, and the number of liver cells undergoing fatty degeneration significantly decreased, while the number of normal liver cells increased. Compared with the control group, the hepatic cord structure of the 300 and 500mg/kg groups was clearly visible, and no obvious inflammatory infiltration was found. The liver cells were uniform in size, intact in morphology, neatly arranged, with uniform cytoplasm and distinct nuclei. The nucleus was located in the center, and there were fewer liver cells squeezed to one side. The hepatic sinusoids were clearly visible, and a small number of red blood cells were visible in the sinusoids. In summary,Bile acids can effectively alleviate hepatic steatosis and restore the normal tissue structure and physiological function of the liver to a certain extent. Adding 300 and 500mg/kg bile acids has a significant effect.

Figure 1. The effect of bile acids on the morphology of the liver in laying hens

The red box represents the selected 400X field of view; The yellow arrow represents fat vacuoles.

A. B, C, and D represent a 40X field of view under a microscope; E. F, G, and H represent the 400X field of view under a microscope.

The effect of bile acids on lipid metabolism in the liver of laying hens

See table 1，As the amount of bile acid added (200, 300, and 500mg/kg) increased, the content of malondialdehyde and triglycerides showed a linear decrease in both the first and second order (P<0.05)。Compared with the control group, the malondialdehyde content in the 300 and 500mg/kg bile acid treatments was significantly reduced (P<0.05), and the malondialdehyde content in the 300 mg/kg bile acid treatment was significantly lower than that in the 200mg/kg bile acid treatment (P<0.05); Compared with the control group, the triglyceride content of 300mg/kg bile acid treatment was significantly reduced (P<0.05).

Table 1. Effects of different levels of bile acids on antioxidant and lipid metabolism in the liver of laying hens

The effect of bile acids on fatty acids in the liver of laying hens

As the amount of bile acid added (200, 300, and 500 mg/kg) increased, C18: The content of 0 showed a linear decrease (P<0.05), while the content of C18:0 and n-6PUFA/n-3PUFA showed a quadratic linear decrease (P<0.05). The content of C18:1n9c and MUFA showed a linear increase (P<0.05), while the content of C18:1n9c, MUFA, and n-3 PUFA showed a quadratic linear increase (P<0.05). Compared with the control group, the C18:0 content and n-6 PUFA/n-3 PUFA content were significantly reduced (P<0.05) in the 300mg/kg bile acid treatment group, while the C18:1n9c, MUFA, and n-3 PUFA content were significantly increased (P<0.05) in the 300mg/kg bile acid treatment group; Compared with the control group, the C18:0 content was significantly reduced in both 200 and 500mg/kg bile acid treatments (P<0.05). All other differences were not significant (P>0.05).

Bile acids affect gene expression in the liver of laying hens

See Figure 2，With the increase of bile acid addition levels (200, 300, and 500 mg/kg), the expression levels of HSL and FABP4 gene mRNA showed a linear increase in both the first and second order (P<0.05); The expression levels of FAS and SCD gene mRNA showed a linear decrease in both the first and second order。Compared with the control group, the mRNA expression levels of HSL and FABP4 genes were significantly increased in each treatment with bile acid addition (P<0.05); Compared with the control group, the mRNA expression levels of FAS and SCD genes were significantly reduced in the 300 mg/kg bile acid treatment group (P<0.05), and the mRNA expression level of SCD gene in the 300 mg/kg bile acid treatment group was significantly lower than that in the 200 mg/kg bile acid treatment group (P<0.05). All other differences were not significant (P>0.05).

Brief summary

The lipid synthesis site of egg yolk is the liver. In order to meet the needs of egg production, the liver often operates at high load and causes serious metabolic burden. The high load operation of laying hens not only leads to the deposition of TC and TG content in the liver, but also affects the composition of liver fatty acids. Compared with unsaturated fatty acids, saturated fatty acids cause greater damage to the liver. In order to alleviate the large amount of lipid deposition in the liver, exogenous substances are often added during production to regulate the synthesis and transport speed of fat in the liver, thereby reducing the content of TC and TG in the liver. This study found that adding bile acids can effectively alleviate hepatic steatosis and restore the normal tissue structure and physiological function of the liver to a certain extent; The content of saturated fatty acids shows a decreasing trend, while the content of monounsaturated fatty acids and n-3 PUFA shows an increasing trend; The content of malondialdehyde and triglycerides significantly decreased; The expression levels of HSL and FABP4 gene mRNA showed an increasing trend, while the expression levels of FAS and SCD gene mRNA showed a decreasing trend, which further proves that adding bile acids can effectively improve the liver health of laying hens.

Study on the Effects of Bile Acids on the Production Performance and Intestinal Liver Function of Egg laying Chickens in the Late Stage of Egg Production

Author: Zhang Yunlong

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