An attempt to use progesterone treated XO mares as embryo recipients

Abstract

SummaryXO mares were evaluated as potential embryo transfer recipients. In the first part of the study, they were treated with oestrogen and progesterone for 10 and 14 consecutive days. During this course of steriod treatment, their endometria changed in histological appearance from anoestrous to dioestrous and their peripheral plasma progesterone levels rose from below 0.3 ng/ml to above 2 ng/ml. Plasma LH concentrations also rose during the period of oestrogen administration but declined again to baseline when progesterone treatment began. Urinary oestrogen concentrations rose and fell in conjunction with oestrogen treatment. In the second part of the study 16 Day 7 embryos were transferred non‐surgically to seven XO mares given daily injections of progesterone and 12 embryos were transferred to eight ovariectomised mares treated similarly with progesterone. Pregnancies were established in five of the ovariectomised mares but not in any of the XO mares. The possible reasons for the failure to establish pregnancy in the XO mares are discussed.