Submitted to: Symposium on Energy and Protein Metabolism and Nutrition
Publication Type: Proceedings
Publication Acceptance Date: 5/10/2010
Publication Date: 9/5/2010
Citation: Baldwin, R.L., Sumner-Thomson, J., Connor, E.E., Li, R.W., Mcleod, K.R., Bequette, B.J. 2010. Hepatic transcriptome of beef steers is differentially modulated by composition of energy-substrate supply in growing beef. In: G.M. Crovetto (Ed.), Energy and Protein Metabolism and Nutrition; Parma, Italy. pp. 313-314. Wageningen Academic Publishers, The Netherlands. Interpretive Summary: Development of improved carcass quality characteristics (higher protein deposition concomitantly with lower fat) while maintaining or improving the efficiency of production is fundamental to the economic stability of the beef industry. Selection for and manipulation of gene expression will likely be a management tool implemented in future production paradigms which will require improved understanding of putative metabolic regulators of tissue accretion. Our objective was to characterize coordinated genomic responses in Liver in response to infusion of nutrients into the gut of growing steers. Gene transcript expression was evaluated by microarray. Following statistical analysis, several hepatic genes appear to be differentially expressed with increased starch flow to the small intestine. Much of the response appears to be associated with signal transduction among the cells of the liver, and growth related changes which is consistent with our current understanding of how the liver responds to increased nutrient delivery in general, by growing in mass. Further evaluation of these gene changes while evaluating the changes in visceral nutrient metabolism from these same steers will increase our understanding of the control of nutrient use efficiency in cattle.
Technical Abstract: To identify important rate-controlling sequences in response to differing macronutrient supplies, 19 beef steers (272.5 ± 17.6 kg initial BW) were fed a forage-based diet and infused per abomasum with either water (Control, n = 4), Casein (n = 5) or Starch (n = 5), or fed Na-propionate (n = 5) for 42-d. Treatments were administered on an equal energy basis (40 kcal/kg metabolic BW). On day 42, steers we killed, mRNA was isolated from liver and prepared for transcriptome profiling. Total RNA for hybridization to the USDA whole-genome array bovine 60-mer custom array was isolated from liver samples collected at slaughter. Quality and concentration of RNA was determined using an Agilent 2100 Bioanalyzer and ND-1000 spectrophotometer, respectively. Probes were labeled per standard procedures outlined by Roche Nimblegen Systems for hybridization to the high-density oligonucleotide microarray at the Microarray Core Facility in Reykjavik, Iceland in one batch of 19 arrays. Two samples did not meet the control requirements for cDNA synthesis yield and quality. Using first principal component analysis, verified by cluster analysis, two additional samples were excluded from ANOVA and differential expression anaylsis (PADE). Remaining samples were used for ANOVA and PADE analysis (3 for Control, 3 for Na Propionate, 4 for Starch and 5 for Casein treatments). Steers receiving nutrient infusion gained more weight (3.6 to 5.2%, P < 0.05) over the 42-d experiment compared to Controls. There were 4713 probes identified as being differentially expressed (P< 0.05). Identification of uniquely differentially expressed genes due to macronutrient infusion and pathway analysis is in progress.