Collection, description and transfer of embryos from cattle 10--16 days after oestrus.

Of 226 donor cattle treated with PMSG to induce superovulation, 76.5% responded with 3 or more ovulations. Flushing at surgery or slaughter 10-16 days after oestrus recovered eggs and embryos that represented 49.3% of the number of ovulations. Of those recovered, 73.3% were embryos, an average yield of 4.0 embryos/treated cow or 4.8 embryo/flushed cow. The location of eggs and embryos was determined in 65 of the donors. Embryos and unfertilized eggs (6.1% of those recovered) were occasionally found in the oviducts. Empty zonae pellucidae were also found in the uterus on all days. The lengths, or diameters, of embryos were extremely variable within days and within donors, but mean values indicated logarithmic growth between Days 10 and 16. Eighty-four synchronous (+/- 1 day) recipients received single embryos, and 51 recipients twin embryos, by surgical transfer. Pregnancies were obtained in recipients up to Day 16 but not on Day 17, indicating the stage by which an embryo must be present to prevent luteolysis. The overall pregnancy rate at Day 42 was 50.4% and further 18.1% of the recipients exhibited extended oestrous cycles. Of 35 recipients that were allowed to go to term, 12 lost their pregnancies, most often between Days 42 and 63.