This study evaluated population trends and biochemical parameters of Sjenica sheep in central and southwestern Serbia to assess their adaptive capacity under extensive systems. Population data (2020–2025) and biochemical analyses of 30 adult sheep from the Pešter Plateau, Valjevo, and Zlatibor were used. The population increased by about 68%, with females comprising over 96%. Most biochemical parameters were within reference ranges, indicating preserved metabolic balance. Moderate variability reflected individual physiological differences. The results confirm good metabolic health and strong adaptation of Sjenica sheep, emphasizing the importance of coordinated breeding and genetic monitoring for long-term conservation.