233 HIGH NUMBERS OF ANTRAL FOLLICLES INFLUENCE THE IN VITRO EMBRYO PRODUCTION, BUT NOT THE CONCEPTION RATE OF FIXED-TIME ARTIFICIAL INSEMINATION IN NELORE CATTLE

Abstract

The aim of this study was to compare the conception rates to fixed-time artificial insemination (FTAI) and in vitro embryo production between Nelore cows with high or low antral follicle counts (AFC). First, multiparous Nelore cows (Bos indicus, n = 547, 40–60 days postpartum) were subjected to synchronization of ovulation. Randomly during their oestrous cycle (Day 0), cows received an intravaginal device containing 1.9 g of P4 (CIDR®) and 2 mg of oestradiol benzoate (Estrogin®), intramuscularly. At device removal (Day 8), cows received 500 µg of PGF_2α (Ciosin®), 300 IU of eCG (Novormon®), and 1 mg of oestradiol cipionate (ECP®), intramusculary. All cows were inseminated 48 h after P4 device removal. Antral follicles = 3 mm were counted using an intravaginal microconvex transducer (Day 0), and cows were assigned to groups of high (G-High, = 25 follicles, n = 183), intermediate (G-Intermediate, 16–20 follicles, n = 183), or low AFC (G-Low, = 10 follicles, n = 181). In another study to compared the in vitro embryo production, Nelore cows (n = 66, 72–96 months) were subjected to ultrasound-guided follicular aspiration using an intravaginal microconvex array transducer (7.5 MHz). The COC were selected and cows were assigned to groups according to the oocyte production: G-High (n = 22, = 40 oocytes), G-Intermediate (n = 25, 18–25 oocytes), or G-Low (n = 19, = 7 oocytes). Previously tested semen from a single bull was used for IVF using a previously described protocol (Silva-Santos et al. 2014 Reprod. Domest. Anim. 49, 228–232). The oocyte and embryo production (viable embryo: grade I, II, III; vitrifiable embryo: grade I, II) were evaluated. The number of follicles was evaluated by Kruskal-Wallis, and the chi-square test was used for data on oocyte and embryo production (P = 0.05). The average follicular population was 30.7 ± 5.7 (G-High), 18.6 ± 1.64 (G-Intermediate), and 7.8 ± 2.4 follicles (G-Low; P < 0.05), but there were no differences in the conception rates among groups (51.9 v. 48.6 v. 58.6%, respectively; P > 0.05). The total number of oocytes recovered were 1109 (G-High), 534 (G-Intermediate), and 101 (G-Low; P < 0.05). The mean number of viable oocytes was 40.4 ± 10.6 (G-High), 14.8 ± 3.0 (G-Intermediate), and 3.8 ± 1.1 (G-Low; P < 0.05) and the percentage of viable oocytes was 80% (G-High), 69% (371/534, G-Intermediate), and 71% (G-Low; P < 0.05). Cleavage rate was 79% (G-High), 74% (348/472, G-Intermediate), and 71% (G-Low; P < 0.05), and blastocyst rate was 42% (G-High), 32% (153/472, G-Intermediate), and 13% (G-Low; P < 0.05). The number of viable embryos was 18.4 ± 6.7 (G-High), 6.1 ± 3.6 (G-Intermediate), and 0.6 ± 0.7 (G-Low; P < 0.05) and the percentage of vitrifiable embryos was 81% (G-High), 77% (118/153, G-Intermediate), and 58% (G-Low; P < 0.05). Therefore, Nelore cows with high oocyte production had ~10-fold higher oocyte production and produced ~30-fold more embryos compared with the low AFC group. In conclusion, AFC had no influence on the conception rates to FTAI; however, Nelore cows with high oocyte production exhibited higher in vitro embryo production.