131 EFFECT OF PROLONGED PROGESTERONE EXPOSURE OF BEEF COWS ON THE EXPRESSION OF OOCYTE DEVELOPMENTAL COMPETENCE-ASSOCIATED GENES

Abstract

Progesterone is a key hormone in reproduction and plays a crucial regulatory role during the oestrous cycle and pregnancy. The effect of progesterone on the developmental competence of bovine oocytes is yet to be fully understood. Molecular tools might provide further information on the role of progesterone on expression of developmentally important genes. The objective of this study was to evaluate the effect of the prolonged exposure of beef cows (days = 32) to different progesterone levels on the expression of genes associated with oocyte developmental competence. Fifteen cows were used in the experiment and were divided in 3 treatment groups (group n = 5). Treatment 1 consisted of no progesterone supplementation, treatment 2 consisted of supplementation by insertion of one controlled internal drug release device (CIDR) per animal, and treatment 3 consisted of supplementation with the insertion of 2 CIDR per animal. All cows were subjected to follicle ablation 4 days before initiation of the experiment. At Day 0, prostaglandin F_2α (PGF_2α, 25 mg of dinoprost tromethamine, i.m., Lutalyze®) was administered and CIDR devices were inserted in cows designated to treatments 2 and 3. Cumulus-oocyte complexes were collected through ovum pickup where follicles >2 mm were aspirated. Samples evaluated were obtained at Day 0, 8, 16, 24, and 32. The oocyte developmental competence-associated genes METAP2, FOXM1, HMGA1 were analysed in the study. Polyadenylate polymerase was used as normalization gene. Relative gene expression was calculated utilising a comparative CT method (2^−ΔΔCT) where data were calculated as fold increase (>1) or decrease (<1) from a calibrator included in each PCR reaction. Mean values of the fold increase/decrease were compared between treatments and were analysed by repeated-measures ANOVA. No statistical difference was detected between treatments at Day 0, 8, 16, 24, or 32 when analysing independent relative expression of oocyte developmental competence-associated genes METAP2, FOXM1, or HMGA1 (P > 0.05). Similarly, no significant differences between treatments was detected in relative expression of METAP2, FOXM1, or HMGA1 across time (P > 0.05). Prolonged exposure of progesterone at different levels does not affect the expression of METAP2, FOXM1, and HMGA1 genes in bovine cumulus-oocyte complexes as indicated by the results of this experiment.