126 A Comparison of Two Different Follicular Coasting Periods for In Vitro Embryo Production in Indian Nelore Cattle

Abstract

Ongole, also known as Nelore (Bos indicus) cattle, are indigenous to the Andhra region in the Prakasam District in the State of Andhra Pradesh in India. A better understanding and utilisation of follicular wave dynamics within this breed would ultimately enhance oocyte and potential embryo production. Therefore, the aim of this study was to evaluate the differences between coasting periods of 24 h (S1) and 36 h (S2) on oocyte recovery, the rate of viable oocytes, cleavage, and Day 7 blastocyst rates of Nelore cattle in India. A total of 58 ovum pick-up (OPU) sessions (29 per treatment) were performed on 32 healthy donor cows that were randomly assigned to 1 of 2 coasting treatments (S1 or S2). Donors were stimulated as follows: 2.5 mL of gonadotropin-releasing hormone (GnRH; Receptal, MSD Animal Health, New Zealand) given IM on Day 1 followed by once-daily descending dose of Folltropin^® (FSH, Vetoquinol, Canada) on Days 3 to 5 for a total of 180 mg. Cumulus-oocyte complexes were collected following OPU on Day 6 either at 24 (S1) or 36 h (S2) following the last FSH injection (coasting period). Donors were subject to OPU 1 to 3 times with a minimum interval of 15 days between procedures from March to April 2017. All 32 donor cows were non-lactating at the time of aspiration and divided equally between treatment groups. A total of 1492 follicles produced 850 total oocytes with oocyte recovery numbers for treatments S1 and S2 (785, 707; 441, 409; respectively). All data were analysed by ANOVA (P < 0.05). The mean number of follicles aspirated from S1 (27 ± 20.2) was not significantly different from that of S2 (24.4 ± 14.4). For S1, 393/441 (89%) quality oocytes were utilised for culture compared with 323/409 (78.9%) for S2, with no differences between rates. Additionally, there were no differences between mean number of oocytes, cleaved embryos, and blastocysts for S1 (15.2 ± 12.7; 9.9 ± 9.2; 4.3 ± 5.4) and S2 (14.1 ± 10; 7.4 ± 6.0; 3.6 ± 3.3; respectively). In conclusion, there were no differences found between 24- or 36-h coasting periods of Nelore cattle undergoing OPU for follicle counts, oocyte recovery, viable oocyte rates, cleavage, and blastocyst rates. Further research is needed to determine whether different stimulation protocols, the use of lactating cows, or coasting periods could alter outcomes.