Fertility indicates the strength of the animal's reproductive function and the ability to have offspring, also known as fertility. It consists of a series of physiological phenomena and many performance indicators: the period of sexual maturity of the female animal, the frequency (number of times) and seasonality of the estrus cycle, the number of ovulations, the fertilization rate of the egg, the conception rate and the number of breedings per fetus, the establishment and maintenance of pregnancy , embryo survival rate, pregnancy duration, childbirth, litter size (delivery rate), litter size per litter, length of lactation, ability to feed the litter, ability to give birth to reproduce!