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Use of sexed semen in conjunction with in vitro embryo production is a potentially efficient means of obtaining offspring of predetermined sex. Here we evaluate a production scheme involving single and bilateral twin transfer of Holstein female embryos to beef cattle recipients. Holstein oocytes were fertilized with the X-bearing fraction of gender-sorted Holstein semen. Cumulus cells were removed with aid of a vortex or microfluidic device (μFD). Half of the vortexed embryos were cultured in KSOMaaBSA (control), as were all μFD embryos. The remaining vortexed embryos were cultured in control medium with 6% avian white yolk (WY). Embryo production and transfer occurred across five replicates. Cows (n = 475) were synchronized using an Ovsynch protocol. They were administered GnRH on Day −9, PGF on Day −2, and GnRH on Day 0. Half of the cows received a CIDR (1.38 g progesterone) with the 1st GnRH injection. The CIDR was removed at the time of PGF treatment. Day 7 Grade 1 blastocysts were transferred fresh 7 days after the 2nd GnRH injection. Control and WY embryos were transferred as ipsilateral singles and bilateral twins; μFD embryos were transferred singly. Pregnancy was diagnosed with ultrasound between 41–46 days and confirmed between 60–90 days; fetal sexing confirmed that 95% of fetuses were female. Effects on embryo survival were analyzed by logistic regression. Chi-square analysis was applied to survival rates. Replication affected embryo survival (P &lt; 0.05). There was no effect of cumulus removal, medium, or CIDR use. Fetal loss between ultrasounds was greater for twin vs. single transfers (30% vs. 15%, respectively; P &lt; 0.01). Probability of embryo survival was estimated to increase ∼0.006 with each increasing day postpartum. Five cases of hydrallantois were detected during the 5th month of gestation for 1 control twin, 1 WY single, and 3 WY twin transfers, originating from 3 replicates. On a production per transfer basis, the proportion of fetuses obtained for single and twin transfers was 30% and 55%, respectively (P &lt; 0.001). Although there was greater embryonic loss for twin compared to single transfers, a higher percentage of cows receiving twins established and maintained pregnancy. Large-scale transfer of IVP Holstein heifer embryos to beef recipients is a feasible production scheme.Table 1.Embryo survival and pregnancy rates

159 TWIN vs. SINGLE TRANSFER OF IVP HOLSTEIN HEIFER EMBRYOS TO BEEF RECIPIENTS