The goal of this project is to test an adeno-associated viral vector (AAV) gene therapy for MSUD in the calf model. MSUD calves will be treated with human-like doses of AAV gene therapy and fed adult MSUD formula until the AAV gene therapy starts to work. Blood levels of BCAA will be monitored. Behavioral testing, brain MRI, and outcome measures will be performed and compared to unaffected calves. The effectiveness of this gene therapy approach for MSUD in cows will be assessed. Results will serve as proof-of-concept for this therapy in humans and provide important data to design and plan a human clinical trial for MSUD gene therapy.