What is the best definition of an estrous cycle?

The estrous cycle refers to the cyclical changes in female reproductive physiology that typically include periods of sexual receptivity, known as estrus or heat. Option B captures this concept perfectly, as it highlights the time frame between one period of sexual receptivity and the next. This cycle can vary in length depending on the species and is characterized by hormonal changes that prepare the female body for potential mating and subsequent reproduction.

In contrast, the other options do not accurately define the estrous cycle. For instance, the periodic shedding of the uterine lining refers to the menstrual cycle, which is different as it involves the endometrium of mammals that experience menstruation rather than estrus. The maturation of eggs is a part of the reproductive cycle but does not encompass the full scope of the estrous cycle, which is more focused on the entire cycle of sexual readiness and receptivity. Lastly, the reproductive cycle of males does not relate to the female estrous cycle and considers different physiological processes altogether. Thus, option B is the most accurate and comprehensive definition of the estrous cycle.