Which grade or score is most closely related to mature size of the animal?

The frame score is most closely related to the mature size of an animal because it specifically evaluates the skeletal structure and overall size potential of livestock. Frame score is determined by measuring various parts of the animal, particularly in cattle, to assess how large the animal will grow to be when it reaches maturity. This score helps predict not only the height and weight of the animal as it matures but also its potential for growth.

Yield grade pertains to the quantity of meat that can be harvested from the animal, focusing more on the carcass characteristics than on the living size. Quality grade assesses the palatability and overall quality of meat based on factors like marbling and maturity rather than the animal's physical dimensions. Condition score evaluates the fat cover and overall body condition of the animal, which provides information on its health and nutritional status rather than its mature size. Therefore, frame score directly focuses on the skeletal frame, making it the appropriate choice for relating to mature animal size.