83 Factors associated with in vitro embryo production in beef cattle

This study aimed to identify factors associated with in vitro embryo production (IVEP) in Bos indicus (Nelore) beef cattle. The database consisted of 2149 donors from three categories (young heifer (YH; n = 640; <15 months old), heifer (HE; n = 390; 15–24 months old), and cow (CO; n = 1119; primiparous and multiparous cows; 3–8 years old)) and was collected from August 2021 to February 2023, from a single embryo production company and a single farm. The statistical analyses were performed using GLIMMIX of SAS 9.4 (P ≤ 0.05). Statistical models included category, body condition score (BCS; scale 1–5), and type of semen (conventional (n = 1140), or sexed (n = 1009)) as fixed effect, and bull as random effect. There was no effect of category and BCS on total, viable, and cleaved oocytes. Although, conventional produced more cleaved oocytes than sexed semen (21.0 ± 0.4 vs 19.5 ± 0.4). There was an effect of category (YH = 79.8^a vs HE = 78.8%^ab vs CO = 76.6%^b; ^a,bP ≤ 0.05) and type of semen (conventional = 82.0 vs sexed = 76.0%) on cleavage rate. The number of viable embryos was affected by category (YH = 5.1 ± 0.3^a vs HE = 5.0 ± 0.4^a vs CO = 6.9 ± 0.3^b) and type of semen (conventional = 6.9 ± 0.2 vs sexed = 5.1 ± 0.1). There was effect of category (YH = 0.28 ± 0.01^a vs HE = 0.30 ± 0.02^a vs CO = 0.36 ± 0.01^b), BCS (<3.0 = 0.28 ± 0.02^a vs 3.0 = 0.28 ± 0.01^a vs 3.5 = 0.31 ± 0.01^a vs 4.0 = 0.33 ± 0.01^b vs >4.0 = 0.36 ± 0.01^c) and type of semen (conventional = 0.34 ± 0.01 vs sexed = 0.29 ± 0.01) on number of embryos per cleaved oocyte. There was effect of category (YH = 0.22 ± 0.01^a vs HE = 0.23 ± 0.01^a vs CO = 0.28 ± 0.01^b), BCS (<3.0 = 0.22 ± 0.01^a vs 3.0 = 0.22 ± 0.01^a vs 3.5 = 0.24 ± 0.01^a vs 4.0 = 0.26 ± 0.01^b vs >4.0 = 0.28 ± 0.01^b) and type of semen (conventional = 0.28 ± 0.01 vs sexed = 0.21 ± 0.00) on number of embryos per cultured oocytes. Therefore, cows had greater cleavage rate, viable embryos, and embryo rate in Bos indicus beef cattle. In addition, donors with BCS >4.0 had greater embryo rate. Furthermore, conventional semen had more cleaved oocytes and viable embryos, and greater cleavage and embryo rate than sexed semen. In conclusion, donor category, BCS, and type of semen on IVEP are critical factors related to reproductive outcomes.

This research was supported by FAPESP#2018/03798–7, CNPq, CAPES, CPEX Embriões and GlobalGen vet science.