Protein Synthesis Is Impaired in Low Compared to Normal Birth Weight Neonatal Pigs

Postnatal growth is reduced in low (LBWT) compared with normal birth weight (NBWT) pigs. The objective of this study was to determine body growth and muscle protein deposition in LBWT and NBWT neonatal pigs. Newborn female pigs (n = 6) were considered NBWT or LBWT when birth weight was within ± 0.5 and -2 SD of litter average. NBWT pigs were fed a control diet, while LBWT pigs were fed an equal amount per kg body weight of either the control diet or the same diet supplemented with 0.68% branched-chain amino acids (BCAA) for 21 d. On day 21, pigs were infused with [2H5]phenylalanine for 8 h, and plasma taken during the last 4 h of tracer infusion. Weight gain was lower for LBWT compared with NBWT pigs throughout the study (P < 0.05). Fat and lean deposition measured by Dual-energy X-ray absorptiometry were lower (P < 0.05) in LBWT compared with their NBWT siblings. Feed conversion and protein efficiency were not different among all groups; however, the efficiency of energy deposition in LBWT pigs was about 20 % lower than in NBWT pigs (P < 0.05). Longissimus dorsi and gastrocnemius muscle weights of LBWT were 52% and 49% of those from NBWT pigs. Protein synthesis rate was lower (P < 0.05) at 30 and 60 min after feeding in LBWT compared with their NBWT littermates, but there were no temporal changes in protein degradation. This resulted in enhanced protein deposition for NBWT as compared to LBWT pigs (P < 0.05). However, there was no effect of BCAA supplementation on growth or protein deposition in LBWT pigs. These results suggest that reduced postnatal growth and muscle protein deposition is due to lower protein synthesis in LBWT compared to NBWT pigs.