Submitted to: Animal
Publication Type: Review Article
Publication Acceptance Date: 9/29/2009
Publication Date: 11/3/2009
Citation: Connor, E.E., Li, R.W., Baldwin, R.L., Li, C. 2009. Gene expression in the digestive tissues of ruminants and their relationships with feeding and digestive processes. Animal. 4(7):993-1007. Interpretive Summary: The relatively recent availability of genome sequence information for many agriculturally-important species has permitted investigations related to the process of digestion in ruminants at the gene level. In this review, recent investigations of expression of candidate genes important in normal function of the ruminant digestive tract are discussed, as well as genes affected by dietary manipulation, growth and development, parasitic infection and disease states. Recent findings from our laboratory are highlighted related to expression of the glucagon-like peptide 2 hormone pathway in the digestive tract of dairy cattle during different stages of development and milk production, gene changes associated with development of the calf rumen during weaning, and genes of the digestive tract responding to a common nematode infection of cattle. In addition, some areas of future investigation are identified.
Technical Abstract: The gastrointestinal tract (GIT) has multiple functions including digestion, nutrient absorption, secretion of hormones, and excretion of wastes. In the ruminant animal, development of this organ system is more complex than that of the monogastric animal due to the necessity to establish a fully functional and differentiated rumen, in which a diverse microbial population of bacteria, fungi and protozoa support fermentation and digestion of dietary fiber. Central to the goal of animal scientists to enhance nutrient uptake and production efficiency of ruminants is the need for a comprehensive understanding of GIT development, as well as conditions that alter the digestion process. The relatively recent availability of genome sequence information has permitted physiological investigations related to the process of digestion for many agriculturally-important species at the gene transcript level. For instance, numerous studies have evaluated the expression of ruminant GIT genes to gain insight into mechanisms involved in normal function, physiology, and development, such as nutrient uptake and transport across the epithelial cell barrier throughout the alimentary canal, maintenance of rumen pH, and regulation of GIT motility and cell proliferation. Further, multiple studies have examined the effects of dietary modification, including feeding of supplemental fat, starch and protein, or a forage- versus concentrate-based diet on expression of critical gene pathways in the gut. In addition, the expression of genes in the GIT in response to disease, such as infection with gastrointestinal parasites, has been investigated. This review will summarize some of the recent scientific literature related to gene expression in the GIT of ruminants, primarily cattle, sheep and goats, as it pertains to normal physiology, and dietary, developmental, and disease effects to provide an overview of critical proteins participating in the overall digestive processes, and their physiological functions. Recent findings from our laboratory will be highlighted also related to expression of the glucagon-like peptide 2 hormone pathway in the GIT of dairy cattle during various stages of development and lactation, alterations in gene pathways associated with rumen development and differentiation in the weaning calf, and genes of the GIT responding to Ostertagia, a common nematode infection of cattle. Finally, prospective areas of investigation will be highlighted.