154 EMBRYO RESPONSE OF SUPEROVULATED HOLSTEIN HEIFERS INSEMINATED WITH X-SORTED FROZEN SPERM

A study was conducted within a commercial embryo transfer program to assess the appropriateness of X-sorted semen in superovulated heifers. Commercial X-sorted semen frozen at a dose of 2 million sperm/straw and unsorted semen frozen at a dose of 20 to 30 million sperm/straw was used in donors according to the owner’s genetic criteria. One-hundred 15- to 18-month-old Holstein heifers were superovulated as follows: Animals received a CIDR device (Pfizer Animal Health, New York, NY, USA) for 13 days. At the time of CIDR insertion and 5 days later, heifers received 2 mL (0.15 mg) of d-cloprostenol (Veteglan, Laboratorios Calier, Spain). Gonadotropin-releasing hormone (GnRH), 200 mcg IM (Gonasyl, SIVA, Spain) was administered twice, 36 hours after the second prostaglandin (PGF) and 24 hours after CIDR removal. Superovulatory treatments with commercial FSH (Pluset, Laboratorios Calier) were initiated 36 hours after the first GnRH, with a total dose of 11.5 mL (575 IU), given twice daily in 10 daily decreasing-dose injections. Luteolysis was induced with 0.15 mg PGF given twice, 12 h before and at the time of CIDR removal. Heifers were randomly assigned to two groups for insemination in the uterine body: Group A (n = 31) heifers were inseminated with 5 straws of X-sorted semen in three inseminations (2 straws at 12 h, 2 straws at 18 h, and 1 straw at 24 h after the last GnRH); Group B (n = 69) heifers were inseminated twice with unsorted semen (one straw at each of 12 and 24 h after the last GnRH). A total of 614 embryos (153 in Group A and 461 in Group B) were collected and frozen. There were no significant differences between groups (Mann–Whitney rank sum test, SigmaStat, Systat Software Inc., San Jose, CA, USA) in the embryo production obtained (Table 1). Eighty-four embryos frozen with ethylene glycol were thawed and transferred; 34 from Group A, where all births were females and 50 from Group B with a 0.54 sex ratio. Pregnancy rates were 55 and 54% in Groups A and B, respectively. In conclusion, with the superovulation and AI schedule utilized in this experiment, the use of X-sorted semen in heifers can achieve reproductive outcomes similar to those obtained with unsexed semen, with the benefit of an increase in females offspring. Table 1.Mean number of recovered ova/embryos, transferable embryos, and unfertilized ova obtained in superovulated Holstein heifers inseminated with X-sorted (Group A) and unsorted (Group B) semen