Summary. Treatment of recipient cows with 100 mg of progesterone daily from Days 1 to 5 of the oestrous cycle increased plasma progesterone compared with vehicle-treated recipients. Embryo transfer to progesterone-treated recipients which showed oestrus 72 h after the donor cows resulted in pregnancy rates at Day 35 similar to those of synchronous (±12 h) recipients (42 vs. 50%). Only 1 of 22 (4·8%) asynchronous (−72 h) vehicle-treated recipients established pregnancy. Similar treatments of cyclic cows with progesterone shortened (P < 0·01) the interoestrous interval by 3·2 days. When assessed on Day 7 of pregnancy, administration of progesterone to superovulated donor cows on Days 1–4 of pregnancy did not affect early embryo development compared with superovulated cows treated with vehicle alone. Plasma progesterone increased rapidly in superovulated cows compared with cows during the oestrous cycle. The results indicate that administration of progesterone early in the oestrous cycle of the recipient can effectively advance uterine receptivity for the transfer of older asynchronous embryos.
Keywords: bovine; embryo; uterus; progesterone
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