The critical period for the maternal recognition of pregnancy in pony mares

Two experiments were performed to deterine the critical time at which the equine blastocyst must be present within the uterus of the mare to prevent regression of the corpus luteum, and thus establish the critical time for the maternal recognition of pregnancy. A non-surgical blastocyst collection technique was developed to study this relationship between the blastocyst and the maternal ovary. Results from these experiments demonstrated that the cyclic life-span of the corpus luteum is not affected by the presence of the blastocyst within the mare's uterus until after Day 14 after ovulation. Luteal function was prolonged when blastocysts were removed on Day 15 or later. The critical period for the maternal recognition of pregnancy in the Pony mare appears to be confined to the period between Days 14 and 16 after ovulation.