Evaluation of organ and skeletal physiological characteristics for improved classification of growth-restricted newborn piglets.

The identification of potentially slow-growing pigs at birth, using both external and internal traits, would enable the early implementation of targeted management and feeding strategies to optimize herd management and improve production efficiency. Twenty-four piglets from six hyperprolific sows were classified into four categories based on birth body weight (BW), body mass index (BMI), and crow-to-rump length (CRL): severe intrauterine growth restriction (sIUGR), low birth weight (LBW), moderate birth weight (MBW), and high birth weight (HBW). Organ weights, computed tomography (CT) measurements, bending tests to assess tibial mechanical and geometric properties, and tibial mineral content analysis were performed to evaluate organ and skeletal physiological characteristics. Severe IUGR piglets exhibited higher brain-to-organ ratios and relative brain weights, which decreased linearly across categories. High birth BW piglets demonstrated 70% more bone volume and a greater proportion of high-density bones than sIUGR piglets, along with the largest cortical area and thickness in tibia measurements. On the other hand, sIUGR showed higher maximum stress, stiffness values, and manganese content in their tibiae compared to other categories. These findings reveal that piglets with varying degrees of IUGR prioritize brain development, exhibit asymmetrical organ growth, and experience impaired ossification and longitudinal bone growth. This study underscores the need to incorporate complementary birth indicators to refine the classification of newborn piglets with different degrees of restriction.