Embryo transfer

 On day 8 after fertilization, grade 1 blastocyst and expanded blastocyst stage embryos

(Robertson and Nelson, 1998) were harvested from culture. Selected embryos were placed into

holding medium [Hepes-TALP containing 10% (v/v) fetal bovine serum and 100 pM 3-

mercaptoethanol] and loaded into 0.25 cc French straws in groups of 7-12 (depending on the

replicate). Embryos were loaded so that similar numbers of blastocyst and expanded blastocyst

stage embryos were placed into each straw across both treatment groups. Once embryos were

loaded, the straws were then placed into a portable incubator set at 390 C and transported to the

farm for transfer to recipients.

 At day 7 after anticipated ovulation, the ovaries of all cows were scanned again using

ultrasonography to determine the presence or absence of a corpus luteum. Cows were selected

for transfer based on 2 criteria: 1) cows that did not have a preovulatory follicle or a corpus

luteum on day 0 but that did have a corpus luteum on day 7 (i.e., cows that ovulated after the

PGF injection but before the 2nd GnRH injection of OvSynch) or 2) cows that had a preovulatory

follicle on day 0 that was replaced by the presence of a corpus luteum on day 7. A total of 62

cows were selected as embryo transfer recipients based on these criteria. Selected recipients

received an epidural block of 5 mL lidocaine (2%) and groups of embryos were then randomly

transferred to the uterine horn ipsilateral to the ovary with a corpus luteum.

Embryo recovery, evaluation and culture

 On day 14 after anticipated ovulation, both the ipsilateral and contralateral uterine horns

of each recipient were flushed with Dulbecco's Phosphate Buffered Saline (DPBS) to recover

embryos. For 3 replicates, recipients were slaughtered, the reproductive tracts were collected

and the uterine horns were flushed with 100 mL of DPS. For 7 replicates, embryos were

recovered using non-surgical embryo recovery techniques. The uterine horns of each recipient