143 Effect of corpus luteum on recovery rate, quality, and in vitro developmental competence of oocytes in Bos indicus dairy cows

Abstract

Assisted reproductive technologies have modernized the dairy industry for the rapid multiplication of superior genetic traits. However, the exploitation of genetics through in vitro embryo production in farm animals has been struggling during the last 3 decades. The presence or absence of a corpus luteum (CL) on ovaries from which cumulus-oocyte complexes were recovered has been shown to affect the quality of oocytes and in vitro embryo production outcome in Bos taurus cows. Similar information is lacking in Bos indicus cows. Therefore, the objectives of the present study were to determine the effect of presence or absence of a CL on recovery rate, quality, and in vitro developmental competence of oocytes in Bos indicus dairy cows. This study was conducted from December 2017 to April 2018. The ovaries were harvested from a local abattoir (Bos indicus; 5- to 8-year-old cows having mixed parity with clinically normal reproductive tracts). These ovaries (n = 750) were divided into 2 groups [(1) CYCLIC (n = 318) and (2) ACYCLIC (n = 432)] based on the presence or absence of mature CL having follicles on either left or right ovaries of slaughtered cows. Blood samples from the jugular vein were collected at slaughter. Serum concentrations of progesterone of CYCLIC and ACYCLIC cows were measured using radioimmunoassay. Mean number of recovered oocytes per ovary and serum concentration of progesterone were compared using PROC TTEST model. However, quality, maturation, cleavage, 8-cell, 16-cell, and morula rates were analysed by PROC FREQ model of Chi-squared. All the data was analysed using SAS (SAS Institute Inc., Cary, NC, USA). Results revealed that the mean serum concentrations of progesterone (4.21 ± 0.4 v. 0.5 ± 0.2 ng mL⁻¹; P < 0.05) were higher in CYCLIC as compared with ACYCLIC cows, respectively. The mean number of oocytes recovered per ovary (6.5 ± 4.5 v. 4.0 ± 4.4; P < 0.05) was higher in CYCLIC than in ACYCLIC cows. The oocytes with grade I+II quality (55.3 v. 47.6%; P < 0.05) were higher, whereas oocytes with grade III+IV quality (44.5 v. 52.4%; P < 0.05) were lower, in CYCLIC as compared with ACYCLIC cows, respectively. Furthermore, cleavage rate (70.9 v. 52.8%; P < 0.05) was higher in CYCLIC than in ACYCLIC cows, respectively. Similarly, the 8-cell (38.5 v. 20.8%; P < 0.05) and 16-cell (20.0 v. 10.9%; P < 0.05) stage embryos were greater in CYCLIC as compared with ACYCLIC cows, respectively. In conclusion, the presence of CL has a beneficial effect on recovery rate, quality, and in vitro embryo production outcomes in Bos indicus dairy cows. It is implied that for ovum pickup, cyclic cows should be preferred.