or early embryonic development,
rather than to events after blastocyst formation. This
conclusion was based on the observations that: (1) fewer
oocytes inseminated with X-sorted sperm cleaved (in the
Florida study) or became blastocysts (in both the Colorado
and Florida studies) than oocytes inseminated with nonsorted
sperm; and (2) there was no difference in pregnancy
rate between TET cows receiving an embryo produced with
X-sorted sperm or an embryo produced with nonsorted
semen. In other studies too, use of X-sorted sperm in vitro
was associated with reduced cleavage and competence to
develop to the blastocyst stage [5,20–22]. The difference in
development of embryos produced with sexed sperm
occurs after the first cell cycle [20,21] although the problem
might be initiated in the first cell cycle.