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Title: DEVELOPMENTAL CHANGES IN KETOGENIC ENZYME GENE EXPRESSION DURING SHEEP RUMEN DEVELOPMENT

Author
item Baldwin, Ransom - Randy
item LANE, MICHELLE - UNIVERSITY OF TEXAS
item JESSE, BARRY - RUTGERS UNVERSITY

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2002
Publication Date: 6/1/2002
Citation: BALDWIN, R.L., LANE, M.A., JESSE, B.W. DEVELOPMENTAL CHANGES IN KETOGENIC ENZYME GENE EXPRESSION DURING SHEEP RUMEN DEVELOPMENT. JOURNAL OF ANIMAL SCIENCE. 2002. vol. 80(6), pp. 1538-44.

Interpretive Summary: Ketogenesis is an important process for ruminants and is the result of the conversion of acetyl-CoA, derived from ruminally produced butyrate to the ketone bodies acetoacetate and á- hydroxybutyrate (BHBA). To determine the time line and dietary effects on enzyme gene expression rumen epithelium, 27 lambs were reared normally and 27 were fed only milk replacer and slaughtered between 1 and 84 d of age. The expression of genes encoding ketone producing enzymes were examined. Two of the enzymes of interest were increased regardless of the treatment of the lamb. One of the enzymes expressed increased at the same time the ketones produced by the lambs tissues increased. In conclusion, development of the ketogenic capacity of the rumen epithelium occurs as the animal ages, regardless of the diet of the lamb. Thus, the expression of the genes encoding the ketogenic enzymes are not affected by the presence of different nutrients in the rumen which result from eating solid feed.

Technical Abstract: Ketogenesis is the conversion of acetyl-CoA to the ketone bodies acetoacetate and á-hydroxybutyrate (BHBA). In the fed ruminant, rumen epithelium produces ketone bodies using acetyl-CoA from mitochondrial oxidation of butyrate produced by the microbial fermentation of feed within the rumen. To determine ontogenic and dietary effects on ketogenic enzyme gene expression in developing lamb rumen epithelium, 27 lambs conventionally reared and 27 milk-fed lambs were slaughtered between 1 and 84 d of age. Also, six milk-fed lambs were weaned (FG) or maintained on milk-replacer with a VFA gavage (VG) until 84 d of age. The expression of genes encoding acetoacetyl-CoA thiolase, and 3-hydroxy-3-methylglutaryl-CoA synthase were examined. Acetoacetyl-CoA thiolase and 3-hydroxy-3- methylglutaryl-CoA synthase mRNA concentrations increased with age independent of diet. 3-Hydroxy-3-methylglutaryl-CoA synthase mRNA levels in rumen epithelium obtained from milk-fed lambs were low before 42 d of age, but a marked increase occurred by 42 d of age. At 84 d of age there were no differences in acetoacetyl-CoA thiolase and 3-hydroxy-3- methylglutaryl-CoA synthase expression due to diet. The pattern of the expression of these genes, in particular, 3-hydroxy-3-methylglutaryl-CoA synthase, parallels the rate of increase in production of BHBA by rumen epithelial cells isolated from the same lambs. In conclusion, development of the ketogenic capacity of the rumen epithelium occurs as the animal ages, regardless of treatment. Thus, the expression of the genes encoding the ketogenic enzymes are not affected by the presence of VFA.