ARTICLE FEED & ADDITIVE MAGAZINE January 2023 59 • Protein synthesis • Improves antioxidant capacity • Improves digestive enzyme activity • Reduces ammonia toxicity • Bone mineralization • Amino acid synthesis • Fat metabolism • Gene expression • Improves fillet quality 1. On growth performances and protein synthesis AKG serves as a crucial supply of glutamine and glutamate for cellular metabolism, which promotes protein synthesis, prevents muscle protein breakdown, and serves as a crucial metabolic fuel for gastrointestinal tract cells. Gln, which makes up more than 60% of the entire amino acid pool, provides an energy source for all types of cells in the organism. As a way, AKG, which is a precursor to Gln, serves as both an important source of energy for intestinal cells and a favoured substrate for enterocytes and other rapidly proliferating cells. Moreover, the transformation of Gln and Glu into ornithine and later arginine, stimulates the release of growth hormone and insulin-like growth factor I. The animal will grow more effectively with these kinds of molecular modifications. Many studies have shown that dietary AKG decreases nitrogen excretion from the body and enhances nitrogen digestion, deposition, and retention, which promotes protein synthesis and helps in animal growth. By increasing the intestinal functions in animals, AKG enhances better digestion and absorption of nutrients. Wang et al., (2016) reported that the development of the intestine was promoted by the AKG supplementation in hybrid sturgeon. Thus, the growth performance was increased by the addition of AKG. In a recent study, 1% AKG supplementation in Juvenile mirror carp (Cyprinus carpio) feed promoted the growth performance, final body weight, weight gain rate, feed intake and phosphorus intake. Pradhan et al., (2021) reported that the combination of L-carnitine and AKG could enhance the growth performance, and nutrient utilization in tilapia. 2. On digestive enzymes The levels of activities of digestive enzymes are used as comparative indicators of growth rate and digestive capacity of the fish. It is speculated that AKG, as an intermediate of TCA, also an intermediate of Glu and Gln, may contribute to ATP homeostasis in the small intestine. By interacting with the glutamine metabolic pathway, AKG can produce glutamine (Gln) which increases the functional surface area of the intestinal mucosa and improve the nutrition absorption. Feeding the 0.75 % AKG diet increased significantly amylase, protease, and lipase in the foregut of grass, when compared with the
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