Luteal function and blastocyst development in ewes following treatment with PGF₂α and GnRH

Luteal function and blastocyst development were compared in ewes treated with GnRH (100 μg) on Day 1 (Day 0 = day of estrus) or in ewes previously induced into estrus with PGF₂α. In Experiment 1, the duration of estrous cycles of ewes previously treated with PGF₂α were longer (P<0.06) than those that received PGF₂α plus GnRH, GnRH alone, or remained untreated (control) ewes. Progesterone concentrations were lower (P<0.07) on Day 1 and higher (P<0.01) on Days 16 and 17 of the estrous cycles following PGF₂α treatment relative to those of the natural (control) cycles. In Experiment 2, blastocysts of ewes treated with PGF₂α were less developed (P<0.06) by Day 13 of pregnancy than those of the control ewes. The GnRH treatment did not influence any of these characteristics. Treatment with PGF₂α delayed luteal formation during the subsequent estrous cycle, increased the duration of the estrous cycle and slowed the rate of blastocyst development relative to GnRH-treated and untreated ewes.