When the sheep are observed by B-ultrasound, when there is no corpus luteum on the ovary at the beginning of superovulation, the number of available embryos is adversely affected due to the increase in the proportion of degenerated embryos; however, when the sheep are observed by B-ultrasound that there is no corpus luteum on the ovary, due to the presence of large follicles, there will also be interactions, and the dominant follicles will have a great impact on the recovery of embryos and the rate of available embryos. To obtain a large number of embryos with good quality through superovulation, progesterone treatment and FSH injection are often combined, and progesterone suppository treatment is continued until the end of FSH injection. The effect of superovulation is not only affected by the follicle group present on the ovary at the beginning of FSH injection, but also by the presence or absence of corpus luteum on the ovary.

Sheep B-ultrasound image

These differences are explained by induction of some factors related to the synchronous estrus scheme. Treatment with progesterone at the same time as superovulation can cause the transformation of growing follicles and dominant follicles on the ovary. These changes can be corrected by the simultaneous secretion of progesterone in the corpus luteum environment. In general, in practice, progesterone suppositories are placed on any day of the unknown estrus cycle of the ewe. According to the treatment of progesterone suppositories, the production of excess progesterone levels (the progesterone released by the progesterone suppository and the progesterone in the corpus luteum are superimposed) and sub-level progesterone content (i.e., the progesterone released by the progesterone suppository) works. When the progesterone suppository is placed, when there is a corpus luteum, the sheep can observe the activity or shortening of the life cycle of the large follicles by B-ultrasound, and when there is no corpus luteum, the activity and life cycle of the large follicles are prolonged. This fact can be explained by the phenomenon that a good superovulation response can be obtained by using two progesterone suppositories during the synchronous treatment in the superovulation scheme. However, even so, a higher progesterone level in the donor is maintained by the progesterone suppository during the entire treatment process, but the superovulation effect is still affected by the fact that when the progesterone suppository is placed, the sheep observes the corpus luteum of the ewe's ovary by B-ultrasound in the early to middle stage, from the middle stage to the late stage, or the follicles are in different developmental stages.

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