In ruminants, body reserves (BR) are mobilized in situations of negative energy balance, including physiological stages with high metabolic challenges. In contrast, BR accretion occurs when nutrient requirements decrease. This dynamic is partly controlled by metabolic patterns, whereas its genetic determinism is still unknown, at least in sheep. The objective of this preliminary study was to estimate genetic parameters for a few key metabolites and hormones involved in sheep BR dynamic. The BR changes over time were monitored over three years on 318 productive Romane ewes reared exclusively in an extensive rangeland. Plasma non-esterified fatty acids (NEFA), beta-hydroxybutyrate (β-OHB) and triiodothyronine (T3) levels were quantified 2 weeks before and 3 weeks after lambing and 2 weeks before mating. Effects of physiological stage, litter size and a parity-year factor were tested to identify main sources of variation. Genetic parameters were estimated using animal mixed model considering independently measurements at each physiological stage. The least square means for NEFA, β-OHB and T3 were significantly (P<0.001) different according to the physiological stage. The levels of NEFA and β-OHB were higher before lambing (0.44±0.01 mmol/l and 39.83±0.80 mg/l, respectively) and decreased until before mating (0.15±0.01 mmol/l and 23.09±0.95 mg/l, respectively). The level of T3 was equivalent before lambing and before mating (around 1.00 ng/ml) and lower than before mating (1.35±0.02 ng/ml). Heritabilities for NEFA, β-OHB and T3 ranged between 0.11±0.12 to 0.29±0.12, 0.21±0.11 to 0.35±0.17 and 0.16±0.11 to 0.38±0.16, respectively, depending on the physiological stage. Genetic correlations between NEFA and β-OHB before lambing and before mating reached 0.89±0.13, and -0.90±0.25, respectively. The T3 was also highly correlated with β-OHB before lambing (-0.70±0.26). These preliminary results suggest that metabolites and hormones involved in BR dynamics are heritable traits. Further measurements on additional ewes are in progress to confirm these results.