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Title: Intestinal and ruminal epithelial and hepatic metabolism regulatory gene expression as affected by forage to concentrate ratio in bulls

Author
item Baldwin, Ransom - Randy
item EL-KADI, S - UNIVERSITY OF KENTUCKY
item MCLEOD, K - UNIVERSITY OF KENTUCKY
item Connor, Erin
item BEQUETTE, B - UNIVERSITY OF MARYLAND

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/10/2007
Publication Date: 9/9/2007
Citation: Baldwin, R.L., El-Kadi, S.W., Mcleod, K.R., Connor, E.E., Bequette, B.J. 2007. Intestinal and ruminal epithelial and hepatic metabolism regulatory gene expression as affected by forage to concentrate ratio in bulls. Symposium Proceedings. pp. 293-294.

Interpretive Summary: In ruminants, we have demonstrated a change in use of amino acids using isolated cell preparations. Few studies describe alterations in gene expression of these important metabolically active tissues in response to changes in feed. Angus bulls (n = 12; 391 ± 34 kg) were randomly assigned to either forage based or concentrate based diets. Feed was offered daily and refusals were weighed. Bulls were weighed weekly and feed offered adjusted accordingly. After the >28 d on diets, bulls were slaughtered and intestine, rumen, and liver tissue samples were collected for determination of gene expression of metabolic regulatory proteins by a highly sensitive analytic tool called, quantitative real-time polymerase chain reaction. Using this procedure we looked at several genes of interest and found that in cattle expression of regulatory genes changes in response to altered nutrient supply when cattle are fed complex rations. This means that in addition to understanding the way that nutrients are absorbed and interact, we can also begin to consider how the genes which regulate nutrient use are affected when diets are prepared. This will ultimately allow for ration formulations which optimize nutrient use for production of milk and meat in balance with excretion of difficult to manage waste matter.

Technical Abstract: In ruminants, we have demonstrated variable rates of oxidation of amino acids using isolated cell preparations. Few studies describe alterations in putative regulatory metabolic gene transcript expression of these metabolically active tissues in response to changes in ration. Angus bulls (n = 12; 391 ± 34 kg) were randomly assigned to two dietary treatments of either 75:25 (HF) or 25:75 (HC) using common orchard grass silage and concentrate ingredients, respecively. Feed was offered daily and refusals were weighed. Bulls were weighed weekly and feed offered adjusted accordingly. After the >28 d on diets, bulls were slaughtered and intestinal and rumen epithelia, and liver harvested for determination of gene expression of putative metabolic regulatory proteins by qRT-PCR including: sodium glucose co-transporter I (SGLT-1), monocarboxylic acid transporter-1 (MCT-1), acetyl/propionyl-CoA synthetase 2 (ACAS2L), butyryl-CoA synthetase 1 (BUCS1), branched chain aminotransferase 2 (BCAT2), branched chain keto acid dehydrogenase (BCKDHA), glutaminase (GLS), glutamate dehydrogenase (GLUD1), glutamic-oxaloacetic transaminase 2 (GOT2), and glucose-6-phosphate dehydrogenase (G6PDH). Total RNA was obtained using RNeasy isolation kits with on-column DNase digestion and quality and concentration were determined. Starting quantities were quantified using a standard curve. By design, dry matter intake was similar between the treatments resulting in 33% greater metabolizable energy intake for the HC vs. HF bulls and average daily gains of 1.6 kg/d and 1.56 kg/d for HC and HF, respectively. Abundance of BCAT2 transcripts were at or below detection and abundance of MCT-1, SGLT-1, ACAS2L, and GLS, while present, were unaffected by treatment. Abundance of BCKDHA transcripts increased in rumen of HF bulls but was unaffected in intestinal epithelium and liver. Abundance of BUCS1 transcripts tended to decrease in rumen and increased in jejunum and liver in HF bulls. Intestinal expression of G6PDH was unaffected by treatment, but rumen and liver abundance was increased in HF bulls. Expression of GOT2 increased in rumen and tended to increase in jejunum in HF bulls but was unaltered in duodenum or ileum. These data demonstrate in cattle differential expression of regulatory genes in response to altered nutrient supply using complex rations.