Embryonic mortality in heifers after artificial insemination and embryo transfer: differences between virgin and repeat breeder heifers.

Embryos were collected from repeat breeder heifers and virgin heifers seven days after insemination, classified and transferred to the uterine horn contralateral to the corpus luteum of synchronised inseminated recipients. Altogether 35 transfers were performed, all reciprocally between repeat breeder heifers and virgin heifers. The recipients were slaughtered either 16 to 17 days or 32 to 35 days after insemination. The survival rate of the native embryos was lower among the repeat breeder heifers than among the virgin heifers both at 16 to 17 days (six of nine vs six of six) and at 32 to 35 days (three of 10 vs seven of 10) after insemination. A higher proportion of embryos transferred from repeat breeder heifers to virgin heifers than from virgin heifers to repeat breeder heifers survived to days 16 to 17 (five of six vs two of nine), while the same proportion of embryos survived to days 32 to 35 (two of 10) in both heifer categories. The results suggest that the uterine environment in repeat breeder heifers is suboptimal for the support of normal embryonic development.