Metabolomic Analysis of the Longissimus muscle revealed differences between Underperforming and Normal Preweaning Growth Piglets.

The present study was designed to determine if normal birth weight pigs that grow poorly during the pre-weaning period have altered skeletal muscle metabolism, as previously reported for intrauterine growth retarded pigs relative to littermates with normal growth rates. Eight pairs of average birth weight pigs (1.57 ± 0.05 kg) were identified that diverged in weight by a minimum of 50 g/day until 21 days of age. At 21 days, slow growing (SG) pigs weighed 5.47 ± 0.22 kg while control (C) littermates weight 6.98 ± 0.28 kg (P < 0.001). Samples of longissimus were collected for metabolomic analysis at day 21. Metabolomic analysis was performed by Metabolon (Durham, NC) using ultrahigh performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS). Analysis of the longissimus from these SG pigs identified 68 metabolites that were increased and 33 that were decreased relative to longissimus from C littermates using matched pairs t-tests for analysis (P < 0.05). A reduction in central carbon metabolism was apparent in longissimus from SG pigs relative to C pigs. Specifically, SG pigs exhibited decreases in several pentose sugars and alcohols, including sedoheptulose 7-phosphate (P = 0.016), 6-phosphogluconate (P = 0.022), ribose 5-phosphate (P = 0.031), and ribitol (P = 0.048); indicative of reduced pentose phosphate shunt activity. Decreases were also apparent in the glycolytic intermediates glycerol 3-phosphate (P < 0.001) and lactate (P = 0.013). The key glycolysis-derived intermediates glucose-6-phosphate (P = 0.015) and fructose-6-phosphate (P = 0.012) were also reduced in longissimus of SG pigs relative to C pigs. Increased levels of carnitine (P = 0.003), acetylcarnitine (P = 0.019) and deoxycarnitine (P = 0.026), coupled with increased levels of several phospholipids (P < 0.05), diacylglycerols (P < 0.05), and sphingolipids (P < 0.05) suggest more fatty acid synthesis and utilization in longissimus of SG pigs than C pigs. Longissimus of SG pigs exhibited higher levels of 3-methylhistidine (P = 0.003), pro-hydroxy-pro (P = 0.034), trans-4-hydroxyproline (P = 0.002), which are associated with increased muscle breakdown and extracellular matrix remodeling. In conclusion, muscle from SG pigs displayed limited accretion of pentose phosphate metabolites, with corresponding increases of many lipid classes that suggest a shift to β-oxidation over carbohydrate oxidation. This further corresponded with increased markers of muscle and collagen breakdown, consistent with a more catabolic state in the SG pig.