A complete bull breeding soundness exam assesses all of the following EXCEPT:

A complete bull breeding soundness exam is designed to evaluate a bull's ability to sire offspring. This assessment generally involves several critical factors associated with reproductive health and physical condition. Among these factors, evaluating libido—essentially the bull's desire to breed—is often considered less reliable or subjective.

While libido is an important aspect of breeding, it is not always systematically measured during the soundness exam, as it can fluctuate due to various factors such as stress, environmental conditions, or even the bull's individual temperament. Instead, the exam focuses on more quantifiable metrics which provide a clearer understanding of the bull's reproductive capabilities.

In contrast, the other elements such as semen quality, testicular size, and physical condition can be accurately assessed and directly impact the bull's breeding soundness. Semen quality is crucial for fertility, while adequate testicular size directly correlates with the production of healthy sperm. Physical condition influences the overall health and stamina of the bull, making it vital for successful breeding.

Therefore, while libido is a component of reproductive performance, it is not an essential or standardized part of the complete bull breeding soundness exam, which explains why it is not assessed in this context.