Embryo production in superovulated Angus cows inseminated four times with sexed-sorted or conventional, frozen-thawed semen.

This study tested the hypothesis that four inseminations of commercially frozen sexed semen (>or=2.1x10(6) sperm per 0.25-mL straw) in superstimulated embryo donors would yield a percentage and quantity of transferable embryos similar to that achieved with conventional frozen semen. Bos taurus, angus cows (n=32), stratified by age and body condition, were randomly allocated to receive four inseminations of frozen-thawed semen, either conventional semen (>or=15x10(6) sperm/straw; Conventional) or sexed semen (>or=2.1x10(6) sperm/straw; Sexed) from one of two AI sires. From 10 to 13 d after estrus, follicle-stimulating hormone (FSH) was given twice-daily, with prostaglandin F(2alpha) given twice on the last day. Cows were inseminated once (1x) at first detected estrus and twice (2x) and once (1x) at 12 and 24h later, respectively, with nonsurgical embryo recovery 7 d after first detected estrus. The study was repeated 30 d later (switch-back experimental design). The total number of ova per flush was similar between Conventional and Sexed treatments (10.9+/-1.8 vs. 10.5+/-1.6), but the number of Grade 1 embryos was greater (P<0.01) for Conventional (4.3+/-0.8 vs. 2.3+/-0.7). Conversely, the mean number of unfertilized ova was greater (P<0.05) for Sexed (5.6+/-1.0 vs. 3.0+/-1.2). There was no significant difference between treatments for numbers of degenerate, Grades 2 or 3, and transferable embryos and no significant differences between bulls in percentage of transferable embryos (44.4% and 46.7%). However, fertilization rates and percentage of transferable embryos were affected (P<0.05) by period and donor. In conclusion, superstimulated donor cows inseminated four times had fewer Grade 1 embryos and more unfertilized ova with sexed versus conventional semen.