## 1 Introduction  
Non-invasive diagnostics and finding biomarkers of disease in humans have been a very active research area [1; 2; 3]. Some of the analytical technologies used for finding biomarkers of human disease are finding their use in livestock [4; 5; 6; 7; 8]. Non-invasive sample collection from diseased cattle using breath [4; 5; 6] and headspace of fecal samples [7] have been reported. In this work, we explore the use of volatile organic compounds (VOCs) emitted from bovine nasal secretions and serum for finding biomarkers for bovine respiratory disease (BRD). BRD is not caused by 'a' pathogen--it is a multi-factorial complex that involves various combinations of physiological stress, animal mismanagement, assorted bacterial and viral pathogens, and inclement weather conditions [9; 10]. BRD is the most costly disease condition found in feedyards in the U.S. with losses occurring in the form of decreased feeding performance, increased death loss and treatment costs, and lower carcass value at the time of harvest [11]. Various strategies have been utilized to mitigate the losses associated with BRD with varying results [9; 12]. Vaccination strategies have been combined with antibiotic therapy to minimize pathogen exposure and spread within groups of calves. Improved nutritional practices have attempted to optimize feed efficiency while minimizing the metabolic effects of sub-acute acidosis. Even with these advancements, the feedlot industry in the U.S. continues to see only marginal improvement in the overall morbidity and mortality levels due to BRD. Recently, interest has grown in the identification of metabolic markers for various disease conditions in cattle using metabolomics. Metabolomics (proteomics) is the study of either primary or secondary metabolites of a biological system and their changes to better understand system responses to disease and other influences or manipulations on that biological system [13; 14]. Body fluids are composed of various electrolytes, hormones, and especially its proteome that may contain information about feeding status, nutritional requirement, and adaptations to diet and environment, and also about the health status of the animal. Biological fluids, oral fluids, serum, and plasma can be harvested and analyzed to map changes to cellular biology to better understand the effect that outside factors have on a biological system. A recent review of the relative strengths and weaknesses of the main proteomic techniques used in human and animal studies is published [13]. These techniques included liquid or gas chromatography-mass spectrometry (GC-MS), matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS), and nuclear magnetic resonance (NMR). GC-MS gives the best overall view of primary metabolism in a biological system. The majority of metabolites found in the GC-MS data are lower molecular weight, primary metabolites, and those from core metabolic processes including amino acid metabolism, fatty acid metabolism, tricarboxylic acid (TCA) cycle, and glycolysis. Saliva has been widely used in swine as a diagnostic sample to monitor disease status and metabolic state [14]. Metabolomic studies involving cattle have utilized milk, rumen fluid, urine, serum, and plasma to evaluate the presence of ketosis, heat stress, odor generation, feed digestion, and transition time in dairy cattle [15; 16; 17; 18; 19]. One study focused on differences in metabolomic profiles between young dairy calves with acute bronchopneumonia and normal contemporaries [20]. Plasma was collected from these calves and NMR was utilized to detect differences between the two groups. These groups had two distinctly different and distinguishable metabolic fingerprints using both water soluble and lipid extracts. Alterations in various metabolites were meaningful for pathogenic mechanisms of calf bronchopneumonia.