What term is defined as the age at which a stallion ejaculate contains a minimum of 1X10 to the 8th total sperm with 10 percent progressive motility?

The term that defines the age at which a stallion's ejaculate contains a minimum concentration of 1X10 to the 8th total sperm with 10 percent progressive motility is puberty. This stage marks the onset of sexual maturity in male horses, indicating that they are capable of reproduction.

During puberty, hormonal changes stimulate the development of the reproductive system, leading to the production of viable sperm. While adolescence typically refers to the broader developmental stage before full maturity, and fertility describes the capability to reproduce successfully, these terms do not specifically relate to the quantitative and qualitative thresholds of sperm production. The pre-adult stage is also a vague term that does not capture the specific indicators of reproductive readiness that are highlighted by the definition provided. Thus, puberty is the most accurate term to describe the age and the associated reproductive capabilities of the stallion.