128 Embryo transfer in Brangus (Bos indicus × Bos taurus) cattle recipients: effects of sire on pregnancy rate using in vitro-produced embryos
M. A. Gutiérrez-Reinoso A B , C. J. Arreseigor C , B. Driedger C , R. Stahringer D and M. Garcia-Herreros EA
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Embryo transfer (ET) efficiency depends on several factors. One of these factors could be the sire fertility which may influence the pregnancy rate (PR). The main objective of the present study was to evaluate the potential effects of different sires used in in vitro-produced embryos on the PR (Day 30 and 60) after embryo transfer in Brangus cattle. A total of 426 transfers were carried out in Brangus cows (Bos indicus × Bos taurus; Age: 4–8 years; body condition score: 3.0–3.5) maintained under the same nutritional, management, and environmental conditions. Ovum pickup (OPU) sessions (n = 57) were carried out in Brangus donors (n = 57; only one OPU session per donor), which were super-stimulated as follows: Day 0: intravaginal CIDR (progesterone (P4) 1.38 g/cow) + intramuscular progesterone (100 mg/cow) + intramuscular 17-β-oestradiol (2 mg/cow); Day 1: Intramuscular equine chorionic gonadotrophin (eCG; 2500 IU/cow); Day 4: OPU. The embryos were produced following a standard IVP protocol (in vitro-matured OPU-derived cumulus–oocyte complexes and then fertilized with conventional unsorted semen) using five different Brangus sires (S) in all the OPU/IVF sessions. All sires were distributed across all donors. The resulting embryos (S1 = 57; S2 = 243; S3 = 40; S4 = 59; S5 = 27) were transferred fresh to oestrous synchronized cows. Recipients were synchronized following a conventional protocol: Day 0: intravaginal CIDR + 2.5 mg intramuscular (IM) oestradiol benzoate E2B + 50 mg of P4 (IM); Day 7: CIDR removal + 500 µg of PGF2a (IM) + 200 IU of eCG (IM); Day 9: 0.004 mg of buserelin acetate (GnRH; IM); Day 16: embryo transfer. The ET was performed in recipients showing oestrus and corpus luteum. Pregnancy diagnosis was carried out using ultrasonography on Day 30 and 60 following embryo transfers. The data were analysed by GLMM/chi-squared (SPSS® 25, IBM Corp.). Differences were observed on PR (Day 30 after transfer) using IVP-derived fresh embryos among sires (S1 = 64.9%, 37/57; S2 = 55.1%, 134/243; S3 = 55.0%, 22/40; S4 = 39.0%, 23/59; S5 = 37.0%, 10/27; P < 0.05). On Day 30 no differences were observed in PR among S1, S2, and S3 (P > 0.05) and between S4 and S5 (P > 0.05); however, differences were observed in PR between S1-S2-S3 and S4-S5 (P < 0.05). On Day 60 after embryo transfer, differences were observed on PR among sires used for IVP (S1 = 45.6%, 26/57; S2 = 42.8%, 104/243; S3 = 32.5%, 13/40; S4 = 27.1%, 16/59; S5 = 25.9%, 7/27; P < 0.05). On Day 60 no differences were observed in PR between S1 and S2 (P > 0.05) and among S3, S4, and S5 (P > 0.05); however, differences were observed in PR between S1-S2 and S3-S4-S5 (P < 0.05). Differences were observed regarding embryo loss rate in S1 (19.3%), S2 (12.3%), S3 (22.5%), S4 (11.9%), and S5 (11.1%) when Day 30 was compared to Day 60 (P < 0.05). No differences were observed in embryo loss between S1 and S3 (P > 0.05) and among S2, S4, and S5 (P > 0.05); however, differences were observed in embryo loss between S3 and S2-S4-S5 (P < 0.05). In conclusion, PR was greater on Day 30 compared to Day 60 after embryo transfer in Brangus recipients irrespective of the sire used. PR was associated with the sire used in the IVP procedure irrespective of the day of gestation. The embryo loss rate increased over time regardless of the sire considered.
