Effect of triiodothyronine on developmental competence of bovine oocytes

Developmental competence of in vitro-matured bovine oocytes is a limiting factor in production of embryos in vitro. Several studies have suggested a potential positive effect of thyroid hormones on cultured oocytes and/or their supporting cells. Therefore, the aim of the present study was to ascertain whether medium supplementation with triiodothyro- nine (T3) improved subsequent developmental competence of in vitro-matured bovine oocytes. For this purpose, we first documented (using reverse transcription PCR) that whereas bovine cumulus cells expressed both thyroid hormone receptor (TR)-a and TRb, immature bovine oocytes expressed TRa only. Thereafter, to test the effects of TH on developmental competence, abattoir-derived oocytes were matured in vitro in a medium containing 0, 25, 50, or 100 nM T3 and subjected to in vitro fertilization. Embryo quality was evaluated by assessing cleavage and blastocyst rates, morphological quality, development kinetics, and total cell number on Day 8 of culture. Notably, addition of 50 or 100 nM T3 to the in vitro maturation medium increased (P 0.05) on gene expression. We concluded that supplementation of bovine oocyte in vitro maturation medium with T3 may have a beneficial effect on the kinetics of embryo development.