Learn how to recognize this condition in your mare.
False pregnancies are not uncommon, so don’t rely exclusively on teasing to determine whether a mare is pregnant.
By Dr. Patrick M. McCue for The American Quarter Horse Journal
In mares, 5 to 10 percent of estrous cycles end in false pregnancies. They’re common enough that you should know how to recognize them.
Normally, a mare ovulates follicles one to two days before she goes out of heat. A corpus luteum, or “CL”, then develops and begins to produce progesterone.
The CL of a nonpregnant mare produces progesterone for about 14 or 15 days during the luteal phase of the estrous cycle. At the end of that phase, the mare’s uterus must determine pregnancy, a process called “maternal recognition of pregnancy.” First, the embryo produces a chemical signal and, second, the uterus detects the signal.
If the uterus doesn’t find that signal, the endometrial lining of the uterus releases prostaglandins that travel through the bloodstream to the ovary and destroy the CL. Progesterone levels drop rapidly, and the mare develops another follicle and returns to heat. This cycle repeats itself multiple times each breeding season in a nonpregnant mare.
If an embryo is present, no prostaglandins are released, the CL is preserved, and more progesterone is produced. Progesterone is a key hormone for maintenance of pregnancy. It also prevents the mare from returning to heat.
In some instances, a nonpregnant mare’s CL can produce progesterone beyond the normal two-week lifespan and a mare won’t return to estrus. The term for persistent progesterone production by a CL is pseudopregnancy, or false pregnancy.
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