Sunday , July 11 , 2010 SYMPOSIA AND ORAL SESSIONS

The aim of this study was to identify new biomarkers in liver for monitoring physiological imbalance and to examine the different coping strategies used during feed restriction (FR) between cows in physiological imbalance and cows metabolically “normal” during early lactation. Twenty-two cows (22–55 DIM) were fed a standard TMR for ad libitum intake. After 5-d, all cows were FR to provide ~40% of NEL requirements based on body weight, milk production and composition by supplementing the standard TMR with 60% wheat straw. After 4-d of FR, cows returned to full feed. Liver biopsies were collected −1 and 3 d relative to FR. Prior to FR, an index of degree of imbalance was calculated for all cows based on plasma fatty acid, ketone, and glucose concentration. A subset of 6 cows classified as having either the greatest (n = 3) or least (n = 3) degree of imbalance were used for iTRAQ-based quantitative profiling in liver using LC/MS/MS. Prior to FR, 8 proteins were differentially expressed (P ≤ 0.05) due to physiological imbalance. Proteins upregulated (6) were involved in amino acid metabolism, gluconeogenesis, and β-oxidation of fatty acids. Feed restriction resulted in 20 proteins differentially expressed between cows in physiological imbalance and cows metabolically ′normal′. Upregulated proteins (8) were involved in β-oxidation of fatty acids and gluconeogenesis whereas downregulated proteins (12) were involved in antioxidant defense and glycine metabolism. This study is the first to identify new biomarkers in liver based on a physiological imbalance index and provide a better understanding of the differences in coping strategies used during FR for cows in physiological imbalance. Screening for relevant markers in more accessible samples (i.e., blood and milk) will help farmers identify cows at risk. Results provide new avenues for future management strategies relating to maintaining animal health and productivity during early lactation.