This study was conducted with the aim to determine the effect of the bovine corpus luteum on in vitro embryo production. Immature cumulus-oocyte complexes (COC) were aspirated from abattoir ovaries from cows (mainly Holstein and dairy crossbred cows and heifers) with (ipsilateral; CL+) and without (contralateral; CL−) corpus luteum (CL), and from cows without CL in any of the ovaries. The average weight of the ovaries from each group was 10.4±0.25, 5.7±0.25, and 6.1±0.25g for CL+, CL−, and C, respectively. The experiment was completed within 12 replicates (100 ovaries per group). The COC were cultured in maturation medium (TCM-199 supplemented with 10% fetal bovine serum, 100µg mL−1 sodium pyruvate, 0.75mg mL−1 of L-glutamine, 4µg mL−1 of FSH-p, 100 µM cysteamine, and 250µg mL−1 of gentamicin) followed by IVF (synthetic oviducal fluid medium supplemented with 10µg mL−1 heparin) and in vitro culture (citrate synthetic oviducal fluid medium). On Day 7 after IVF, the embryos were evaluated and classified into morulae (M), early blastocysts (EB), regular blastocysts (RB), expanded blastocysts (ExB), and hatched blastocysts (HB), and the embryos with quality 1 (according to IETS criteria) were recorded. Data were analysed by logistic regression and general linear model of SAS (SAS Institute Inc., Cary, NC, USA), and means were compared by the least squares means method. Results of cleavage, embryo rate at Day 7, and rates of M+EB, RB, ExB, and HB are shown in Table 1. The number of embryos per ovary was greater (P<0.01) in CL+ (1.16±0.11) than in CL− (0.45±0.15) and C (0.55±0.15). Also, the number of embryos per cultured oocyte was significantly greater in CL+ than in CL− and C (0.27±0.02v. 0.14±0.03 and 0.15±0.03, respectively; P<0.01). The results of this study reveal that the presence of the corpus luteum in the ovary at the time of the oocyte recovery affects the developmental capacity of the bovine embryos, and such influence probably occur through intraovarian interactions.
Table 1.Effect of bovine corpus luteum on embryo production
