An experiment was designed to evaluate in vitro embryo production following the use of frozen-thawed conventional or Y-sexed semen from a single Brangus and a single Braford bull of proven fertility. Semen was obtained by splitting the same ejaculate to be frozen directly or sex-sorted and then frozen. Oocytes were obtained from 69 ultrasound-guided follicle aspiration (ovum pickup) sessions performed at random stages of the oestrous cycle without superstimulation in 24 Brangus and 10 Braford cows and heifers. Viable oocytes (n = 1120) were matured in TCM-199 medium with NaHCO3 and supplemented with 1% fetal bovine serum. Frozen-thawed sperm from the Brangus and Braford bulls were selected with Percoll for IVF, capacitated in Fert Medium, and used at a final concentration of sperm per milliliter for conventional (non-sexed) semen and 2 × 106 sperm mL–1 for Y-sexed semen. After 16 h (sexed) or 18 h (conventional) of co-incubation with oocytes in Fert Medium, presumptive zygotes were denuded and cultured in SOF supplemented with 0.4% BSA under oil at 37°C, 5% CO2, and saturated humidity for 7 days. The total number of oocytes matured and fertilized from the Brangus donors was 538 and 318 for conventional and sexed semen, respectively. The total numbers of oocytes matured and fertilized from the Braford donors were 139 and 125 for conventional and sexed semen, respectively. Data were compared by ANOVA for mixed models, using breed and type of semen as fixed variables and cow (i.d.) as a random variable. Cleavage and blastocyst rates were first transformed by square root and then analysed by ANOVA for mixed models. Mean (± s.e.m.) number of total viable oocytes collected, cleaved zygotes, and blastocysts produced per ovum pickup session did not differ (P = 0.18) between breeds (Brangus: 17.1 ± 1.6, 10.0 ± 0.9, and 6.2 ± 0.7 v. Braford: 13.9 ± 2.8, 7.6 ± 1.5, and 4.0 ± 0.8), and there was no breed × semen interaction on the mean number of cleaved zygotes and blastocysts produced. However, the mean (± s.e.m.) number of cleaved zygotes and blastocysts produced was significantly higher (P < 0.05) when the oocytes were fertilized with conventional semen (10.7 ± 1.2 and 6.5 ± 0.8) than with sexed semen (7.7 ± 0.7 and 4.3 ± 0.6). The mean cleavage rate was also significantly higher (P < 0.05) when the oocytes were fertilized with conventional semen (76.8 ± 3.9) than with sexed semen (54.1 ± 4.2). Blastocyst rate tended to be higher (P = 0.1) with conventional semen (40.5 ± 3.3) than with sexed semen (33.6 ± 4.2). Although in vitro production may be the preferred alternative for the production of embryos of a known sex, the number of blastocysts produced might be reduced as compared with the use of non-sexed semen from the same bull.
An experiment was designed to evaluate in vivo and in vitro embryo production following the use of frozen–thawed conventional or Y-sexed semen from a Brangus bull with known high fertility. For in vivo embryo production, Brangus heifers (n = 12) were superovulated twice in a crossover design and inseminated with sexed or conventional semen. On Day 0, all heifers received an intravaginal progesterone device (DIB 1 g, Syntex S.A., Buenos Aires, Argentina) and 2.5 mg oestradiol benzoate and 50 mg progesterone (Progestar, Syntex S.A.) by intramuscular injection (IM). On Day 4, heifers were superstimulated with 200 mg of NIH-FSH-P1 Folltropin-V (Bioniche Animal Health, Belleville, Ontario, Canada) in twice-daily decreasing doses over 4 days. In the a.m. and p.m. of Day 6, all heifers received PGF2a (Ciclase, Syntex) and DIBs were removed in the p.m.. In the a.m. of Day 8, heifers received 100 μg de Gonadolerin (Gonasyn, Syntex S.A.) and were randomly allocated to receive either one straw of conventional semen (24 × 106 sperm per dose) 12 and 24 h later or two straws of sexed semen (2.4 × 106 sperm per dose) 18 and 24 h after GnRH. Ova/embryos were collected nonsurgically on Day 15 and evaluated following IETS recommendations. Means were compared by t-test. Mean ( ± s.e.m.) number of ova/embryos, fertilized ova, and transferable embryos were 14.8 ± 2.7, 9.4 ± 1.8, and 7.1 ± 1.7 v. 16.8 ± 3.1, 9.9 ± 2.5, and 8.1 ± 2.0 for donors inseminated with conventional or sexed semen, respectively (P > 0.6). For in vitro production, oocytes were obtained from 50 ultrasound-guided follicle aspiration (OPU) sessions that was performed at random stages of the oestrous cycle and without superstimulation in 22 Brangus cows and heifers. Oocytes were classified and matured in TCM-199 medium with NaHCO3 and supplemented with 1% fetal bovine serum. Semen samples from the same bull used for in vivo embryo production were selected using Percoll and capacitated in Fert medium and used at a final concentration of sperm/mL for nonsexed semen and 2 × 106 sperm mL–1 for sexed semen. After 16 h (sexed) or 18 h (conventional) in Fert medium, zygotes were denuded and cultured in SOF supplemented with 0.4% BSA under oil at 37°C, 5% CO2 and saturated humidity for 7 days. The total number of oocytes matured and fertilized was 528 and 318 for conventional and sexed semen, respectively. Means were compared by t-test and proportions by chi-squared test. Mean (± s.e.m.) number of cleaved zygotes and blastocysts produced per OPU session did not differ between conventional (11.0 ± 1.4 and 7.1 ± 1.0) and sexed (8.7 ± 0.8 and 4.9 ± 0.7; P > 0.2) semen. However, the proportion of cleaved zygotes and blastocysts produced were significantly higher (P < 0.05) with conventional semen (61.2%; 329/538 and 39.4%; 212/538) than with sexed semen (54.4%; 173/318 and 30.8%; 98/318), respectively. In conclusion, comparable number of embryos can be obtained in vivo with sexed or conventional semen from a bull with proven high fertility. However, the proportion of blastocysts produced in vitro is likely to be reduced following the use of sexed as compared with conventional semen from the same bull.
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