Effects of Glycine Supplementation on Creatine Synthesis and Growth of Intrauterine Growth Restricted Pigs (Sus scrofa domesticus) Post-weaning
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2021-08-02
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Abstract
This study was designed to test the hypothesis that dietary glycine (Gly) supplementation would improve the growth rate and survivability of post-weaning growing pigs through improved creatine synthesis. Pigs were obtained at weaning (21 d) and divided according to weight as either intrauterine growth restricted (IUGR) or normal, and then assigned randomly to treatment with a dietary supplement of either1% Gly or 1.19% alanine (Ala, isonitrogenous control). Pigs were slaughtered at market weight (188 d) and tissue samples were obtained to determine activities of creatine-synthetic enzymes, and expression of their respective mRNAs. Carcass quality was assessed at the time of slaughter.
Normal pigs receiving dietary Gly and Ala had similar growth rates, final live body weights, and carcass quality. However, dietary Gly supplementation increased growth rate and final body weight (P < 0.05), and improved carcass quality of IUGR pigs. Further, metabolic analyses of tissues from all groups revealed that Gly supplementation increased creatine and creatine-phosphate concentrations in semimembranosus muscle, pancreas, and kidneys of IUGR and normal pigs (P < 0.05). Concentrations of creatine were greater (P < 0.05) in livers of IUGR pigs receiving Gly supplementation, but were similar in plasma from all pigs.
Enzymatic activities and expression of mRNAs for creatine-synthetic enzymes also increased in response to Gly supplementation. Arginine:glycine amidinotransferase (AGAT) activity was greater (P < 0.05) in kidneys of Gly-treated IUGR pigs, and expression of AGAT mRNA followed a similar pattern. Guanidinoacetate N-methyltransferase (GAMT) activity was greater (P < 0.05) in the pancreas of Gly-treated IUGR and normal pigs, and greater in pancreases than in all other tissues analyzed (P < 0.05). While GAMT activity was unchanged in the liver (P > 0.05), GAMT mRNA expression was greater (P < 0.01) for Gly-treated IUGR pigs. The activities and expression of mRNAs for both AGAT and GAMT were lowest in all tissues analyzed from IUGR control pigs. Expression of creatine kinase mRNA was not different due to treatment group or tissue analyzed. Dietary Gly increased (P < 0.05) expression of mTOR mRNA in the kidney and skeletal muscle.
Results of this study indicate that: (1) dietary Gly supplementation can improve the growth and carcass quality of IUGR pigs; (2) IUGR pigs are less able to synthesize creatine beginning at the pre-translational level, but have similar abilities to express creatine kinase an store creatine as creatine-phosphate in tissues analyzed; (3) the rate of creatine synthesis can be enhanced through dietary Gly supplementation; (4) Gly stimulates mTOR expression in kidney and skeletal muscle of post-weaning IUGR and normal pigs. Collectively, these results indicate that dietary Gly supplementation is vital for IUGR pigs to synthesize sufficient creatine and it provides a novel means to manage IUGR pigs.
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intrauterine growth restriction, IUGR, swine, amino acids, nutrition, glycine, growth, creatine