Simple SummaryTo understand the developmental changes in hare femora, this study aimed to examine the mechanical properties, mineralization, and general geometric properties of the thigh bone (femur) throughout the growth and maturation process. The study involved analyzing the strength, stiffness, bone mineral density, and structure of the femur in both young and adult hares. Additionally, the study sought to establish a connection between bone properties and the ecological functions of hares in their natural habitats. Understanding the changes in hare femora as they grow and mature is crucial for many reasons as it provides valuable insights into the effects of aging on wild hares, shedding light on their adaptability and survival strategies.AbstractLagomorphs, which include hares, rabbits, and pikas, are herbivorous animals renowned for their exceptional running abilities. The femur, the largest and strongest bone in their bodies, plays a crucial role in supporting their weight and facilitating movement. This study aimed to investigate the structural and functional changes in the femora of hares during their development in a sex-dependent manner, and the influence of aging on femur structure and function. Various mechanical properties, including stiffness and strength, as well as densitometry and morphology, were evaluated. The study was conducted onn= 24 hares collected from a hunting district in the Lublin region of Poland and divided into four groups: young females, adult females, young males and adult males (n= 6 animals each). Dual-energy X-ray absorptiometry (DXA) was used to measure bone mineral content (BMC) and bone mineral density (BMD), and a three-point bending test was performed to assess mechanical properties. The findings revealed age-related differences in bone properties, with adult males exhibiting increased BMC, and BMD compared to young males. Geometrical properties of the femora mid-diaphysis, such as cortical index and cross-sectional area, remained relatively unchanged during maturation. Regarding mechanical properties, the femora of young males exhibited higher elastic work compared to those of young females, while the femora of adult males exhibited higher elastic and breaking work than those of adult females. The stiffness of femora was higher in adult females compared to young females. The results provide insights into the development and aging of hare femora and contribute to our understanding of the relationship between bone mechanical properties, musculoskeletal system, and aging in the wild. This knowledge can inform animal husbandry practices in captivity and enhance our broader understanding of the ecological functions of lagomorphs.