142 Effect of follicular size on oocyte recovery rate, quality, and in vitro developmental competency following maturation, fertilization, and culturing in Bos indicus cows

Abstract

Applied reproductive technologies include AI, multiple ovulation and embryo transfer, IVF, cloning, ovum pickup, and zygote intra-fallopian tube transfer in farm animals. Modern commercialized dairy farming is ever more relying on in vitro embryo production for maximal utilisation of superior genetics of female animals. Follicular size influenced the quality of the oocytes and their in vitro developmental competence in Bos taurus cows. However, this information is lacking in Bos indicus cows. Therefore, the objectives of the present study were to determine the effect of follicular size on recovery rate, quality, and in vitro developmental competence of the oocytes in Bos indicus cows. The ovaries (n = 508) of 5- to 8-years-old Bos indicus cows, body condition score 2.75 ± 0.25, having mixed parity and clinically normal reproductive tracts, were collected. These follicles on the ovaries were divided into 2 groups based on their size: (1) <6 mm diameter and (2) ≥6 mm diameter. The data on recovery; quality; maturation; cleavage rates; 4-cell, 8-cell, and 16-cell stages; and morula rate were analysed by Chi-squared test using SPSS version 20 software (IBM Corp., Armonk, NY, USA, 2016) system for windows. Results revealed that oocytes with grade I+II quality (68.4 v. 42.1%; P < 0.05) were higher, whereas grade III+IV quality (31.6 v. 57.5%; P < 0.05) were lower, in ≥6 mm as compared with <6 mm groups, respectively. Moreover, the 4-cell (34.5 v. 18.7%), 8-cell (15.4 v. 7.7%), 16-cell (8.7 v. 2.2%) stages and morula rate (4.5 v. 0.3%) were higher (P < 0.05) in ≥6 mm as compared with <6 mm groups, respectively. However, the maturation and cleavage rates did not differ (P > 0.05) between both groups. It is concluded that oocytes having follicle size ≥6 mm have better quality in terms of morphological grades and in vitro developmental competence in Bos indicus cows. It is implied that for maximum production of embryos through ovum pickup, the most appropriate follicular size for aspiration is ≥6 mm.