Which term refers to the ratio of muscling and leanness in swine?

The term that refers to the ratio of muscling and leanness in swine is “composition.” This term encompasses the overall make-up of an animal, particularly how much muscle compared to fat it contains. In the context of livestock selection and evaluation, understanding an animal's composition is crucial because it directly affects meat quality and yield. A higher muscle composition suggests that the animal will provide a greater proportion of lean meat, which is desirable in the market.

On the other hand, body type conveys a general physical appearance or conformation of an animal but does not specifically address the ratios of muscle to fat. Fat content focuses solely on the amount of fat in the animal, which, while related to the overall body composition, does not fully capture the muscling aspect alongside leanness. Body fat percentage specifically measures the amount of fat relative to the total body weight but lacks the comprehensive context of muscularity that “composition” provides. Thus, "composition" is the most accurate term to describe the balance between muscle and fat in swine.