The rumen plays an essential role in the physiology and production of agriculturally important ruminants such as cattle. Functions of the rumen include fermentation, absorption, metabolism, and protection. Cattle are, however, not born with a functional rumen, and the rumen undergoes considerable changes in size, histology, physiology, and transcriptome from birth to adulthood. In this review, we discuss these changes in detail, the factors that affect these changes, and the potential molecular and cellular mechanisms that mediate these changes. The introduction of solid feed to the rumen is essential for rumen growth and functional development in post-weaning calves. Increasing evidence suggests that solid feed stimulates rumen growth and functional development through butyric acid and other volatile fatty acids (VFAs) produced by microbial fermentation of feed in the rumen and that VFAs stimulate rumen growth and functional development through hormones such as insulin and insulin-like growth factor I (IGF-I) or through direct actions on energy production, chromatin modification, and gene expression. Given the role of the rumen in ruminant physiology and performance, it is important to further study the cellular, molecular, genomic, and epigenomic mechanisms that control rumen growth and development in postnatal ruminants. A better understanding of these mechanisms could lead to the development of novel strategies to enhance the growth and development of the rumen and thereby the productivity and health of cattle and other agriculturally important ruminants.

Summary: This study compared the gene expression of mammary tissue from lactating dairy cows exposed to controlled heat stress conditions with cows housed in a thermoneutral condition. The intake of thermoneutral cows was matched to that of heat-stressed cows. Heat stress activated stress-response genes while suppressing genes associated with DNA repair and mitochondrial function. These findings reveal cellular disruptions in the mammary gland that may contribute to a daily milk production loss of 4.35 kg.

Intramuscular fat (IMF) refers to the adipose tissue located between muscle fibers and is a major determinant of meat quality in cattle. The cellular origin of bovine intramuscular adipocytes remains unclear. Therefore, the objective of this study was to investigate this origin. We derived single-preadipocyte clones from IMF and subcutaneous fat (SF) of cattle through single-cell cloning and subsequent validation of their potential to differentiate into adipocytes. Transcriptomic analysis of selected single-preadipocyte clones revealed that although both IMF- and SF-derived preadipocyte clones expressed classical preadipocyte markers such as PDGFRA, DLK1, and ZNF423, they differed significantly in global gene expression profile. Notably, many muscle-specific genes (e.g., MYOG, MB, and MYH3) were expressed at high levels in IMF-derived preadipocyte clones while not expressed in SF-derived clones. Functional enrichment analysis of differentially expressed genes between IMF- and SF-derived preadipocyte clones indicated that many muscle-related functions were enriched in the former. Furthermore, high-level expression of muscle-specific genes persisted in mature adipocytes differentiated from IMF-derived preadipocyte clones. We also found that bovine satellite cells, the widely considered progenitor cells of myocytes in postnatal animals, had the ability to form both myocytes and adipocytes under respective differentiation conditions. Based on these findings, we conclude that in cattle, at least some intramuscular adipocytes are derived from satellite cells.

Skeletal muscle undergoes extensive developmental and functional changes during the transition from neonatal to adult stages, but the biological processes and regulatory mechanisms underlying these changes remain incompletely understood. In this study, we integrated RNA-seq and H3K27ac ChIP-seq analyses to characterize transcriptional and epigenomic changes during muscle maturation in neonatal and adult Angus-cross cattle. RNA-seq analysis of longissimus muscle identified 2785 differentially expressed genes (DEGs) between neonatal and adult muscles. Adult muscle showed increased expression of genes associated with muscle maturation, whereas neonatal muscle exhibited higher activity of pathways related to energy metabolism and protein translation. H3K27ac profiling revealed extensive remodeling of active regulatory elements during muscle maturation, including stage-specific enhancers and super-enhancers. Motif enrichment analysis indicated distinct transcription factor networks associated with neonatal- and adult-specific regulatory landscapes. Neonatal muscle-specific enhancers were enriched for motifs of myogenic regulators, including MYOD1, MYOG, SIX family members, and ASCL2, whereas adult muscle-specific enhancers showed increased enrichment of the MEF2 family members. Integration of transcriptomic and epigenomic datasets identified stage-specific enhancers associated with genes involved in neonatal and adult muscle functions. Together, these findings demonstrate that the transition from neonatal to adult muscle is accompanied by coordinated changes in transcriptional programs and enhancer landscapes, providing new insights into the regulatory mechanisms underlying skeletal muscle maturation.