Under B-ultrasound examination, ewes show a certain pattern of estrus and ovulation under normal fat conditions. After sexual maturity, follicles begin to form on the surface of the ovaries of ewes, which gradually grow and produce more follicle hormones. When the secretion in the blood reaches a certain amount, ewes show signs of estrus. When the follicles develop to a certain extent, ovulation occurs. Under the observation of B-ultrasound in Boxianglai sheep, an adult female goat usually releases 4-8 mature eggs per estrus period and 1-2 eggs per estrus period. The ewe usually begins ovulation 20-26 hours after the onset of estrus. After the egg is released, it can survive in the mother's fallopian tube for about 8-12 hours. If the egg encounters strong male sperm in the first third of the fallopian tube during this period, fertilization can occur. If the egg exceeds this period, it will age and lose its ability to fertilize.

To ensure that the mature eggs released by the ewe meet the sperm in the first third of the fallopian tube and fertilize, it is also necessary to ensure that the male sheep's sperm arrive at the fertilization site in a timely manner. After mating or insemination of ewes, it usually takes 2-3 hours for sperm to reach the first third of the fallopian tube, and sperm can maintain fertilization ability in the mother's reproductive tract for 10-18 hours. Based on this calculation, the suitable time for mating ewes is 2-3 hours before ovulation, which is 18-26 hours after the onset of estrus in ewes. In the actual process of mating or fertilizing estrus ewes, if the ewes mate or fertilize too early, the vitality of sperm will have decreased by the time the ovaries ovulate; If the ewe is mated or fertilized too late, when the sperm reaches the fallopian tube, the egg has lost its vitality, which will lead to a decrease in the pregnancy rate of the ewe during the estrus period or a decrease in the number of lambs born in one litter.