102 In Vitro Embryo Production and Oocyte Quality in Bos indicus Beef Cows Selected for Fertility Characteristics

Abstract

Embryo production may be enhanced when associated with cows selected on the basis of fertility markers, which should be easy to measure, such as antral follicle count (AFC) and genital tract morphometrics. The objective was to evaluate the effects of AFC class on oocyte 24-h outcome and in vitro embryo production in Bos indicus beef cows. Brahman (n = 151) cows (2-13 years old, 344-803 kg of BW, and 7-9 BCS). Low (LAFC), intermediate (IAFC), and high (HAFC) antral follicle classes were defined as follows: LAFC ≤ 30; IAFC 30-49; and HAFC ≥50 AFC. All follicles ≥3 mm in diameter were aspirated by conventional ovum pick-up technique. Only cumulus–oocyte complexes with at least 2 layers of granulosa cells and homogeneous cytoplasm were used for in vitro culture. They were matured in TCM-199 plus supplements for 24 h at 38.7°C in a 5% CO₂ humidified atmosphere. After 24 h of maturation, a subset of oocytes (n = 319) was fixed and analysed under fluorescent microscopy and oocyte outcome was evaluated by classification, as follows: germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I/anaphase I/telophase I (MIAITI), and metaphase II (MII). The second subset of oocytes (n = 797) was fertilized in Ferti-TALP (10-15 oocytes per 60-µL drop) with frozen–thawed semen (18-22 h at 38.7°C in 5% CO₂ after Percoll) from a single bull previously tested for good in vitro fertility. Presumptive zygotes were cultivated in CR2 medium for 48 h at 37.8°C in 5% CO₂. For the remaining 96 h, embryos were transferred to 10% FCS-supplemented TCM-199 drops until the final evaluation. Data were analysed by the GENMOD, GLM, and CORR procedures of SAS (SAS Institute Inc., Cary, NC, USA). Viable oocytes, total embryos, and embryo production efficiency (viable oocyte/total embryos produced; P < 0.05) to AFC in various degrees (r² = 0.87, 0.86, 0.30, respectively). The proportion of oocytes in GV, GVBD, MIAITI, and MII were different (P < 0.05) between LAFC, IAFC, and HAFC classes [GV: 12.3% (13/106)^a, 3.1% (3/96)^a and 4.3% (5/117)^b, respectively]; [GVBD: 32.1% (34/106)^a, 8.3% (8/96)^a and 6.0 (7/117)^b]; [MIAITI: 14.2% (15/106)^a, 26.0% (25/96)^b and 8.5% (10/117)^c, respectively] and [MII: 41.5% (44/106)^b, 62.5% (60/96)^a and 81.2% (95/117)^c, respectively). In conclusion, high AFC is positively related to better in vitro embryo fertility and to 24-h oocyte outcome after in vitro maturation.