Endometrial Cups

When we are asked how many foals we will be having at Halfpint Hollow any given year, we only know how many we expect.  Births are never guaranteed, even when the jennets have been pregnancy tested.  Earlier this year an ultra sound showed Sunee Fox to be pregnant.  She never showed heat, so seemed fine until her due date came and went with no baby...She didn't even start bagging up like they normally do 4-6 weeks ahead of foaling.  We called the vet back for another ultra sound.  No baby!  Couldn't wrap our heads around why we saw no heats in the interim.  Then we learned from our vet about endometrial cups.

For those of you who love learning the why's of what is going on with our miniature donkeys, I will summarize what was passed on to me by our veterinarian, Dr. Anna Wildgrube.

Scientists refer to Day 0-14 as when a jennet is not in heat,  She then comes in what is called "standing heat" (will stand for a jack to breed her) Day 14-18.  If successfully bred, an embryo forms and the jennet is considered officially pregnant Day 21-365 (yes, for 12 months).

Three to four weeks after being bred (Day 36-38) the placenta produces endometrial cups which embed into the endometrial lining of the uterus.  I have read that these help prevent the dam's immune system from attacking the embryo/fetus.  Dr. Anna says if the embryo/fetus aborts once the cups are in place and before Day 150, the endometrial cups continue to give off hormones that make the jennet's system still believe she is pregnant.  Hence, no heats.

If there is no abortion during this window of time, the fetus will start taking over the mother's production of progesterone (Day 120-150).   The endometrial cups will remain until the fetus is producing sufficient progesterone for survival, then disintegrate.  If this transition goes well, a healthy little foal will be born seven months later.  We are hoping this happens for Sunee Fox next year!