Dietary Glucosamine: Effects and Mechanisms in Relation to Production Performance, Eggshell Quality, and Liver Health of Aged Laying Hens

The aim of this study is to investigate the effects and mechanisms of GS in relation to the production performance, eggshell quality, and liver health of aged laying hens. A total of 144 elderly laying hens were randomly divided into a control group, a 0.15% GS group, and a 0.35% GS group and fed for 4 weeks. The experimental results revealed that GS can significantly improve the laying rate, eggshell strength, and eggshell thickness of aged laying hens and reduce the feed-to-egg ratio (<i>p</i> < 0.05). Specifically, 0.35% GS can alleviate symptoms of hepatic steatosis; significantly reduce the levels of AST, TG, and MDA in serum; and increase the levels of ALB and GSH-Px (<i>p</i> < 0.05). The sequencing results demonstrated that GS significantly upregulated the expression of fatty acid breakdown and antioxidant genes, such as <i>PPARA</i>, <i>ACOX1</i>, <i>GSTT1</i>, and <i>CAT</i>, in the liver, while downregulating the expression of fatty acid synthesis and inflammatory genes such as <i>PPARG</i>, <i>FASN</i>, <i>TGFBR2</i>, and <i>TNF-α</i> (<i>p</i> < 0.05). Meanwhile, GS also increased the expression of uterine eggshell matrix protein genes (<i>p</i> < 0.05). In summary, GS improves liver health by regulating fatty acid metabolism, inflammation, and antioxidant pathways and enhances eggshell quality by promoting eggshell matrix protein synthesis.