93 EFFECT OF SEASON ON QUALITY OF OOCYTES, RESULTS OF IN VITRO MATURATION, AND SOMATIC CELL NUCLEAR TRANSFER IN SWAMP BUFFALO

Abstract

Reproductive activity in swamp buffalo is characterized by a clearly demonstrated anestrus season. The aim of the present study was to evaluate season effect on the oocyte collection, in vitro maturation, and somatic cell nuclear transfer. The ovaries collected from a slaughterhouse were divided into 3 groups according to the collection period: (1) G1: from January to April; G2: from May to August, which is characterized by higher climate temperature and low reproductive activity; and G3: from September to December. Cumulus–oocyte complexes (COCs) were aspirated from follicles 2-6 mm in diameter using an 18-gauge needle, washed in HEPES-buffered TCM-199 (Sigma-Aldrich, St Louis, MO, USA), and classified following 3 different quality levels: A (with 4–6 layers of cumulus cells), B (with 2–3 layers of cumulus cells), and C (few or without cumulus cells). The oocytes of A and B categories were used for IVM in maturation media currently used in cattle (TCM-199 medium + 10% fetal bovine serum) with an increase of FSH concentration (30 µg mL^-1) and estradiol-17β (3 µg mL^-1). Maturation was carried out at 39°C in a water-saturated incubator, under 5% CO₂ for 22 h. The oocytes were observed for the cumulus expanding and the presence of polar body (PB). The oocytes with PB were used for further enucleation and cell nuclear transfer using buffalo quiescent fibroblast cells and the technique described previously (Nguyen et al. 2000 Theriogenology 53, 235). The percentages of intact and fused oocytes as well as reconstructed embryos developed to blastocyst stage were compared for the oocytes from G1 and G2. The results indicated that the average number of good quality COCs collected per ovary for the G1, G2, and G3 period were 6.00 ± 4.08 (n = 426), 2.93 ± 2.55 (n = 346), and 4.78 ± 1.05 (n = 445), respectively. The percentages of A and B oocytes were 62.4% (1.58 ± 0.51 vs. 2.17 ± 1.54), 63.2% (0.90 ± 0.32 vs. 0.95 ± 0.50), and 54.7% (1.12 ± 0.25 vs. 1.49 ± 0.53), respectively; the maturation rate was 55.08%, 56.28%, and 52.16%, respectively. There were no significant differences between G1 and G2 in the percentage of intact and fused oocytes (93.7% and 59% for G1; 100% and 60% for G2, respectively), but the rate of embryos developed to blastocyst stage was higher for oocytes from G1 (18.5% vs. 10.2%). In conclusion, in swamp buffalo, the hot season affected significantly the number of oocytes collected per animal and the subsequent results of somatic cell nuclear transfer. The optimal period for working with buffalo oocyte is from January to April.

This work was aupported by a grant from the Vietnam-Italy 3AB3 Project.