PS3-14. Dietary Protein Level Modulates the Transcriptomic Response to Birth Weight in Artificially Reared Piglets

Abstract During the past three decades, increasing litter sizes in Danish pig herds have resulted in a greater proportion of low-birth-weight (LBW) piglets. Many experience intrauterine growth restriction, leading to impaired postnatal growth, altered organ development, and disrupted metabolism. These physiological impairments are often accompanied by changes in tissue-specific gene expression regulating nutrient utilization, energy metabolism, and cellular growth. Transcriptomic profiling offers a valuable approach to elucidating the molecular mechanisms underlying these impairments and identifying pathways responsive to early dietary interventions. The small intestine (SI), liver, and skeletal muscle are key metabolic organs where transcriptional adaptations may determine the ability of LBW piglets to mitigate impairments when dietary protein supply is sufficient. This study aimed to investigate how dietary protein level modulated gene expression and biological pathways in LBW and normal-birth-weight (NBW) piglets, hypothesizing that a high-protein milk replacer (MR) would attenuate birth weight–related metabolic differences in relevant tissues. Forty piglets ((Yorkshire × Landrace) × Duroc) were removed from the sow within 12 h post-partum and allocated by birth weight class (BWC) (LBW 1.0 kg; NBW ≥ 1.0 kg) to one of four RescueDeck units (n = 10 per group). Piglets were hand-fed sow colostrum and subsequently reared artificially with ad libitum access to high-fat (HF) MRs differing in crude protein content. Two groups (LBW and NBW) received a high-protein MR throughout (HFHP0; 22.2% CP, 32% fat DM), while the other two groups received a lower-protein MR (18% CP, 32% fat DM) from day 0–9 before switching to the high-protein MR from day 10–23 (HFHP10). On day 23, piglets were euthanized, and tissues from the distal SI, liver, and semitendinosus muscle were collected for transcriptomic profiling. RNA sequencing (Illumina NovaSeqX, 150 bp paired-end) was performed, and differential expression analyzed using DESeq2 (adjusted P 0.05). Gene set enrichment analysis (Reactome GSEA; q 0.05) identified affected pathways. Milk replacer treatment and BWC significantly affected intestinal gene expression, with 218 differentially expressed genes (DEGs) between LBW and NBW piglets in HFHP10 compared with only two in HFHP0 (adjusted P 0.05), demonstrating a strong MR × BWC interaction. Enriched pathways (FDR 0.05) in LBW piglets fed a high-protein MR included pathways related to cell cycle regulation and protein synthesis, indicating an enhanced growth capacity. Fewer DEGs were detected in liver and muscle, though pathways linked to protein metabolism, immune function, and energy regulation were similarly modulated. In conclusion, a high-protein MR attenuated birth weight–related transcriptional differences and activated pathways associated with cellular growth and metabolic recovery in LBW piglets. These results suggest that early provision of a high-protein diet can partially normalize molecular processes underlying the impaired development of LBW piglets, thereby improving their growth potential.