Effect of different early weaning regimens for calves on adipogenic gene expression in Hanwoo loin at the fattening stage

Early weaning (EW) of calves using a high energy diet to encourage a higher carcass yield through early postnatal metabolic imprinting events may be used as a feeding strategy to improve beef quality. To better understand the importance of nutritional feeding in EW calves, 2-week-old Korean calves were fed with different diets for 10 weeks. After this period, all calves were fed with the same diet for 22 months and then biopsied. We used the RNA-seq technique to investigate the genes and gene networks involved in these treatments. A total of 32,226 fragments were sequenced among the treatments. Overall, 102, 181, and 191 genes showing differential expression levels for T1 (milk replacement + concentrate), T2 (milk replacement + concentrate + roughages), and T3 (milk replacement + concentrate +30% starch) treatments were identified, respectively (FDR < 0.05). In GO enrichment analysis, many biological pathways, including cellular processes, biological regulation, and metabolic processes, were found to be significantly enriched with differentially expressed genes (DEGs) in groups T2 and T3. Many DEGs from T2 and T3 groups were highly enriched in various gene ontology terms related to developmental processes. KEGG pathway analysis found the following: T2 showed changes in the PPAR signaling pathway, regulation of the actin cytoskeleton, biosynthesis of unsaturated fatty acids, and WNT signaling pathway, whereas T3 showed changes in the tight junction, insulin signaling, mTOR signaling, and hypertrophic cardiomyopathy pathways, with both groups showing changes in the adipocytokine signaling pathway. A group of 10 genes strongly associated with adipogenesis and muscle development showed greatly different expression in qRT-PCR, particularly in the T2 and T3 dietary groups. The results suggested that feeding concentrate and roughages (T2) as well as a high starch diet (T3) after EW enhanced the fat content in loin muscle. These results allowed us to identify the nutrition metabolic imprinting effects that cause energy utilization and fat accumulation in loin muscle and give valuable information about the importance of nutrition in the EW stage of calves.