Fertility in lactating dairy cows following timed embryo transfer with fresh in vitro-produced embryos derived from conventional or sex-sorted semen

The objectives of this study were to (1) compare in vitro embryo production using conventional (CONV) or sex-sorted (SS) semen for in vitro fertilization (IVF) of oocytes collected from elite genetic merit dairy and beef donors, and (2) compare pregnancy per embryo transfer (P/ET) in lactating dairy cows following transfer of fresh dairy or beef embryos derived from CONV or SS semen. Oocytes were collected once weekly for a period of 4 successive weeks using ultrasound-guided transvaginal ovum pick-up from the ovaries of elite beef (Angus, n = 37) and dairy (Holstein-Friesian, n = 51) heifers and cows. Following in vitro maturation, oocytes were fertilized with frozen-thawed CONV or SS semen from a panel of beef (n = 6) or dairy (n = 9) sires of proven fertility and cultured in vitro to the blastocyst stage. A total of 507 grade 1 blastocysts (n = 468 fresh, n = 39 frozen-thawed) were transferred to lactating Holstein-Friesian recipients that had been synchronized using a 10-d progesterone-Ovsynch protocol. Recipients were blocked based on parity, DIM, and Economic Breeding Index, and randomly assigned to receive a single beef-CONV, beef-SS, dairy-CONV, or dairy-SS embryo. Pregnancy diagnosis was carried out using transrectal ultrasound on d 32 after synchronized estrus and confirmed on d 63. Pregnancy loss was characterized as loss between d 32 and 63. The number of oocytes recovered per ovum pick-up session (14.9 vs. 8.1), blastocyst yield (28.7% vs. 16.1%) and the number of blastocysts produced per IVF session (2.8 vs. 1.0) were greater for beef donors than dairy donors. Overall, blastocyst yield and the number of blastocysts produced per IVF were similar for CONV (20.0% and 1.7) and SS (24.7% and 2.1) semen. Pregnancy per ET on d 32 and 63 was not different between beef and dairy embryos (d 32: 55.3% and 61.3%; d 63: 46.4% and 56.0%, respectively) or between embryos derived from CONV and SS semen (d 32: 58.8% and 57.9%; d 63: 50.1% and 52.3%, respectively). Pregnancy loss was not different between dairy and beef embryos or between embryos derived from CONV and SS semen. There was no association between serum progesterone concentration on d 7 and pregnancy rate on d 32 or d 63. In conclusion, oocyte recovery and blastocyst development were greater for beef donors compared with dairy donors. Blastocyst development was similar when CONV and SS were used for IVF, and P/ET was similar for dairy and beef embryos and for embryos derived from CONV and SS semen.