Postnatal Growth and Development of the Rumen: Integrating Physiological and Molecular Insights

Abstract

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.

Keywords: IGF-I; cattle; feed; rumen; volatile fatty acid.

Figure 4

The size of rumen papillae in different age groups of cattle. Data obtained, grouped, and interpreted from these publications [13,83,84,85,86,87,88,89,90].

Figure 1

Macroscopic view of the internal surface of the rumen. (A) The rumen of a newborn calf; (B) The rumen of an adult steer. Note that compared to the newborn rumen, the inner surface of the adult rumen is covered with large rumen papillae.

Figure 2

(A) Microscopic view of the rumen wall. The section was cut from the rumen of a newborn calf and stained with hematoxylin and eosin. a: rumen papilla; b: mucosal and submucosal layer; c: muscular layer; d: serosal layer. (B) Schematic representation of different cellular layers of the rumen epithelium.

Figure 3

Schematic representation of absorption and metabolism of volatile fatty acids. CA: carbonic anhydrase; VFA: volatile fatty acids; ACSS1: acyl-CoA synthetase short-chain family member 1; ACADS: acyl-CoA dehydrogenase short-chain; ECHS1: enoyl-CoA hydratase, short chain 1; ACAT1: acetyl-CoA acetyltransferase 1; EHHADH: enoyl-CoA hydratase and 3-hydroxyacyl CoA dehydrogenase; HMGCS2: 3-hydroxy-3-methylglutaryl-CoA synthase 2; HMGCL: 3-hydroxy-3-methylglutaryl-CoA lyase; OXCT1: 3-oxoacid CoA-transferase 1; BDH1: 3-hydroxybutyrate dehydrogenase 1; SDH: succinate dehydrogenase; MDH: malate dehydrogenase; LDH: lactate dehydrogenase.