The Role of Placental Development in Determining Birth Weight and Growth Performance of Lambs

The placenta plays a central role in regulating fetal growth and is a key determinant of lamb birth weight and postnatal growth performance. In sheep, variation in placental traits influences not only neonatal outcomes but also subsequent growth trajectories, supporting the concept of developmental programming. This review summarizes current knowledge on major placental traits, including placental weight, cotyledon number, cotyledon size and surface area, and indices of placental efficiency, and evaluates their associations with lamb birth weight and postnatal growth. Evidence indicates that placental mass alone does not adequately reflect placental function, whereas cotyledon-based traits and placental efficiency provide more informative indicators of fetal growth capacity. Relationships between placental traits and growth outcomes are strongly influenced by litter size, dam parity, and breed. This review highlights key knowledge gaps and emphasizes the need for standardized placental phenotyping and integrative research approaches to improve understanding of early-life determinants of growth performance in sheep.