Abstract
Liver injury threatens the overall health of an organism, as it is the core organ of the animal body. Liver metabolism is affected by numerous factors, with dietary energy level being a crucial one. Therefore, the present study aimed to evaluate hepatic injury and to describe its metabolic mechanism in ruminants fed diets with different dietary energy levels. A total of 25 Yunnan semi-fine wool sheep were fed diets with five dietary metabolic energy levels and were randomly assigned to five groups as follows: low energy (LE), medium–low energy (MLE), medium energy (ME), medium–high energy (MHE), and high energy (HE). The results revealed that the average optical density (AOD) of lipid droplets in the LE, MLE, and HE groups was higher than that in the ME and MHE groups. The enzyme activity of alanine aminotransferase (ALT) was the lowest in the ME group. An increase in dietary energy level promoted the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity and altered the malondialdehyde (MDA) and protein carbonyl (PCO) concentration quadratically. In addition, both high and low dietary energy levels upregulated the mRNA abundance of proinflammatory cytokine interleukin (IL)-1β, nuclear factor-kappa B (NF-κB), and tumor necrosis factor (TNF)-α. Metabonomic analysis revealed that 142, 77, 65, and 108 differential metabolites were detected in the LE, MLE, MHE, and HE groups, compared with ME group respectively. These metabolites were involved in various biochemical pathways, such as glycolipid, bile acid, and lipid metabolism. In conclusion, both high and low dietary energy levels caused hepatic injury. Section staining and metabonomic results revealed that hepatic injury might be caused by altered metabolism and lipid accumulation induced by lipid mobilization.
Highlights
Yunnan semi-fine wool sheep, characterized by optimal reproductive performance, stable genetic performance, strong adaptability, and excellent meat performance and shearing capacity, is an important breed in the development of China’s livestock industry [1]
The concentration of lipid droplets was higher in the low energy (LE), medium–low energy (MLE), and high energy (HE) groups than in the medium energy (ME) and medium–high energy (MHE) groups
The quantitative analysis of average optical density (AOD) values (Figure 1F) revealed that dietary energy levels had a significant effect on the AOD of liver lipid droplets (p < 0.05), TABLE 2 | The effects of dietary energy level on liver weight and index of Yunnan semi-fine wool sheep
Summary
Yunnan semi-fine wool sheep, characterized by optimal reproductive performance, stable genetic performance, strong adaptability, and excellent meat performance and shearing capacity, is an important breed in the development of China’s livestock industry [1]. Several studies have reported that dietary energy concentration exerts an important effect on the development of ruminant organs, with the liver being the most significantly affected [3]. Fatty liver is a reversible disease, with large amounts of triglycerides or lipid droplets accumulating in hepatocytes through steatosis, which adversely affects the development, health, and reproduction of cows [8, 9]. Hepatic lipid accumulation in animals fed diets with low energy levels has not been reported yet. Studies on fatty liver disease in dairy cows have reported a similar insufficient energy intake condition, which suggests that lipid accumulation is frequently observed in the liver of animals fed diets with low energy levels [12]. It is necessary to systematically assess the effects of dietary energy levels on hepatic health in Yunnan semi-fine wool sheep to understand their metabolism
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