EFFICIENCY OF NUTRIENT USE IN CATTLE:IDENTIFICATION OF CRITICAL PHYSIOLOGIC AND GENOMIC REGULATORY PATHWAYS
Title: Characterization of the longissimus lumborum transcriptome response to adding propionate to the diet of growing Angus beef steers
Submitted to: Physiological Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2012
Publication Date: March 27, 2012
Citation: Baldwin, R.L., Li, R.W., Li, C., Song, J., Bequette, B.J. 2012. Characterization of the longissimus lumborum transcriptome response to adding propionate to the diet of growing Angus beef steers. Physiological Genomics. 44:543-550. DOI:10.1152/physiolgenomics.
Interpretive Summary: Central to the development of an economically sustainable beef industry is the ability to produce desirable carcass composition (e.g. higher protein, lower fat) while maintaining high rates of efficient growth. However, balancing for nutritional efficiency, animal health, and reducing negative environmental impacts, is also of increasing importance for sustainability. Our long term objectives are to elucidate the control of whole animal macronutrient utilization such that we can improve nutrient use and product quality in ruminants. Nutritionally, changes observed in muscle tissue gene expression are affected directly and indirectly by nutrients absorbed. The effects of propionate, a principle product absorbed from the rumen, was studied in light of its potential for altering nutrient use efficiency by affecting changes in the metabolism of cattle. Rates of protein gain in muscle tissue were observed and changes in the genes expressed were affected. Specifically, increases in lipid metabolism specific genes may be indicative of the physiological status of the growing steer and response to added energy in the form of short-chain fatty acids (propionate).
Development of novel approaches to use nutritional management paradigms which enhance the rate of gain as well as qualitative characteristics of beef carcass development has the potential to impact not only production efficiency and nutrient use efficiency but also nutrient losses to the environment. Development of these approaches requires an enhanced understanding of the mechanisms controlling muscle tissue accretion in addition to selective marker development. We used Eight Wye Black Angus beef steers (272.5 ± 17.6 kg initial body weight ) fed a forage-based pelleted diet alone (Control; n=4) or supplemented with sodium-propionate included (PRO; n = 4) for 42-d. High quality RNA was extracted from the longissimus dorsi and subjected to transcriptome sequencing using RNA-seq technology with approximately 44.04 million sequences per sample generated. Trimmed reads were aligned to the bovine reference genome (Btau4.0, release 63) and a total of 12,406,168 ±1,278,398 (mean ± SD) and 16,343,549 ± 4,360,916 uniquely mapped reads from control and propionate treatment groups, respectively, were subject to further analysis using edger. Candidates selected were further filtered with a stringent false discovery rate cutoff (FDR <5%) to account for multiple testing. Differentially-expressed genes (203) in the transcriptome were further analyzed using GO analysis (GOseq). Of the 153 candidate genes at FDR <5%, 74 and 36 were up-regulated and down- regulated, respectively. Twelve GO pathways were identified including: Cancer, Endrocrine System Disorders, Gastrointestinal Disease, Genetic Disorders, Hepatic System Disease, Lipid Metabolism, Small Molecule Biochemistry, Carbohydrate metabolism, Molecular Transport, Cellular Development, Connective Tissue Development & Function and Tissue Morphology. Notably, changes in lipid metabolism specific genes reflected both increased oxidative capacity as well as lipid synthetic capacity related genes were prevalent in many of these selected pathways. These observations are consistent with expected enhancements in lean tissue accretion patterns exhibited in steers where a ruminal fermentation results in high propionate relative to other short chain fatty acids. Alterations in muscle tissue lipid metabolism related gene networks are also consistent with enhanced cell formation and functional (protein synthesis, and lipogenic vs. lipolytic activities in muscle) levels warrant further investigation.