Rhodococcus equi (R. equi) pneumonia is a leading cause of disease in young foals. It can cause chronic illness, joint infection, or death, posing a major threat to animal welfare and future performance. While antibodies are known to help prevent R. equi, the specific types that offer the best protection, and how they are passed from mare to foal, remain poorly understood. This project addresses these gaps as follows; in Aim 1, we will define the most protective antibody features using functional assays on samples from hyperimmune plasma and infected foals. In Aim 2, we will study how these protective antibodies are transferred via colostrum to the foal's bloodstream. Together, these aims will inform future development of improved maternal vaccination and antibody-based strategies to protect foals during this high-risk period. The findings will directly support improved foal health and performance outcomes for the equine industry.