Characteristics of embryos from repeat breeder and virgin heifers.

The characteristics of 7-day-old embryos non-surgically collected from 35 repeat breeder heifers (RBH) and 24 virgin heifers (VH) were compared by repeated observations within each animal. A higher incidence of the embryos collected from the VH was classified as normal and had reached a more advanced developmental stage than embryos from the RBH. Nearly all VH yielded normal (N) embryos, but morphologically deviated (MD) or degenerated embryos (D) appeared occasionally in many VH. The RBH group contained three subgroups of animals. One group of RBH yielded a high percent of N embryos. A second group yielded mostly MD or D embryos with an occasional N embryo, and the third group only D embryos or no embryos. Heifers from which no embryos were recovered on day 7 yielded uncleaved ova, apparently retarded embryos or no embryos when slaughtered three days after insemination. It is concluded that retarded embryonic development may be a common factor for most RBH. The embryo morphology and the degree of retardation differ among animals and between oestrous periods in the same animal.