The objective was to compare the conception rates for FTAI and in vitro embryo production between Nelore cows with different antral follicle counts (AFC = number of follicles <= 3 mm in diameter in the ovaries). Nelore cows (n = 547) were subjected to ovulation synchronization. Randomly during the estrous cycle (D0), cows received an intravaginal device containing 1.9 g P4 (CIDR (R)) and 2 mg BE (Estrogin (R)), IM. When the device was removed (D8), the cows received 500 mu g PGF2 alpha(Ciosie (R)), 300 IU eCG (Novormon (R)) and 1 mg EC (ECP (R)), IM. All cows were inseminated 48 h after P4 device removal. Antral follicles >= 3 mm were counted using an intravaginal microconvex transducer (D0), and the cows were assigned to high (G-High, >= 25 follicles, n = 183), intermediate (G-Intermediate, 16-20 follicles, n = 183) or low AFC groups (G-Low, <= 10 follicles, n = 181). In another experiment, COCs were retrieved by OPU from Nelore cows (n = 66), which were assigned to groups according to oocyte production: G-High (n = 22, >= 40 oocytes), G-Intermediate (n = 25,18-25 oocytes) or G -Low (n = 19, <= 7 oocytes). All COCs from the same cow were cultured individually (maximum of 25 COCs per drop) and then in vitro fertilized using thawed frozen sperm (2 x 10(8)/dose) from a Nelore sire of known fertility. The data were analyzed using a Kruskal-Wallis and a Chi-square test (P <= 0.05). There was no difference in the conception rates after FTAI between Nelore cows with high, intermediate or low AFC (51.9 vs. 48.6 vs. 58.6%). 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). Therefore, AFC had no influence on the conception rates for FTAI; however, Nelore cows with high oocyte production exhibited better in vitro embryo production. (C) 2015 Elsevier B.V. All rights reserved.
