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Role of Dietary Glycine in the Growth of Pigs (Sus scrofa) and Hybrid Striped Bass (Morone saxatilis × Morone chrysops)
Abstract
Three series of experiments were designed to test the hypothesis that dietary glycine supplementation could improve the growth of postweaning pigs and hybrid striped bass (HSB) fed diets containing soybean meal (SBM) as the major protein source by increasing glutathione and creatine synthesis in tissues. In Experiment 1, pigs with intrauterine growth restriction (IUGR) or normal birth weights (NBW) were weaned at 21 days of age and then fed a corn- and SBM-based diet supplemented with either 1% glycine or 1.19% alanine (isonitrogenous control). Pigs were slaughtered at market weight (189–195 days of age) and tissues were obtained for metabolic studies, assays of enzymatic activities, and determination of the mTOR signaling pathway. In Experiment 2, HSB of similar size (a mean initial body weight of 5.3 g) were fed for 56 days a SBM (58%)-based basal diet supplemented with either 0%, 1%, or 2% of glycine, with L-alanine serving as the isonitrogenous control; at the end of the feeding trial, blood and other tissues were collected for laboratory analyses. Experiment 3 was conducted in the same manner as Experiment 2, except that the mean initial body weight of HSB was 111 g, there were 4 fish per tank, and the rates of oxidation of L-glutamate, L-glutamine, L-aspartate, and glycine in tissues were determined.
Results of Experiment 1 showed that the final BW and the gain:feed ratio of IUGR pigs were 13.4 kg and 4.4% lower (P < 0.05) than those for NBW pigs, respectively, with no difference (P > 0.05) in feed intake between the two groups of pigs. Compared with the 0%-glycine group, dietary glycine supplementation increased (P ˂ 0.05) the final BW and gain:feed ratio of pigs by 3.8 kg and 10.8%, respectively. Dietary glycine supplementation increased (P ˂ 0.05) concentrations of 1) glycine in the plasma and all tissues of pigs; and 2) glutathione plus glutathione disulfide in the plasma, liver, and jejunum of IUGR pigs. Glycine supplementation also increased (P ˂ 0.05) the mechanistic target of rapamycin (mTOR) signaling pathway in the skeletal muscle and jejunum of pigs, based on the elevated levels of phosphorylated p70S6 kinase and phosphorylated 4E-binding protein 1. Results of Experiments 2 and 3 revealed that the final body weight of fish fed the 1%-glycine diet was increased (P ˂ 0.05), compared with the 0%-glycine diet. Dietary glycine supplementation increased (P ˂ 0.05) the concentrations of 1) glycine in the plasma and all tissues of HSB; 2) glutathione plus glutathione disulfide in the plasma, liver, and proximal intestine; and 3) creatine plus phosphocreatine in tissues, particularly skeletal muscle.
Overall, the results of this study indicate that both pigs and HSB cannot synthesize sufficient glycine when fed SBM-based diets. Thus, supplementing glycine to these diets is necessary for the optimal growth and health of the animals. Glycine is a nutritionally essential amino acid for both IUGR pigs and juvenile HSB.
Citation
He, Wenliang (2023). Role of Dietary Glycine in the Growth of Pigs (Sus scrofa) and Hybrid Striped Bass (Morone saxatilis × Morone chrysops). Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /200067.