Phantom Pregnancy

Last night Biscuit's new owner asked that we come and see what can be bothering her. She kicked out when they tried to clean her feet and was pulling her ears back when grooming her around her tummy.

Her feet were done on Saturday just before the show and therefore they were worried it was her feet.

When we got there her tummy is standing out but she does not show any signs of colic. When trotting her she is sound. However when we touched her around her tummy and hind legs she got very upset. Even though it is not confirmed it seems like she has a phantom pregnancy. She used to go into season every so often and with the stallion across the road we could not understand why she called to him but did not go into season.

I therefore did some research to understand phantom pregnancy and therefore would like to share:

Even though a mare is not pregnant, her body tells her that she is, and all of her reproductive systems react accordingly. She does not come into season, and her body begins preparations for housing and nourishing a fetus that doesn't exist. This is called phantom or false pregnancy.

There are a number of other terms that are used to describe false pregnancy in the mare. They include prolonged luteal activity, persistence of the corpus luteum, prolonged luteal phase, prolonged diestrus, pseudopregnancy, pseudocyesis, and spurious pregnancy.

Whatever the term used, the condition is the same. The mare's body has been given a signal that a pregnancy exists when it does not.

Dealing with a phantom pregnancy was more difficult in the past than it is today. The arrival on the equine medical scene of the diagnostic ultrasound has made the practitioner's work much easier. The administration of the appropriate drug therapy usually brings about a successful resolution.

To understand the phantom pregnancy it is required to understand the role of prostaglandin in the reproductive process.

Estrous cycle of the mare:

The estrous cycle controls when a mare is sexually receptive toward a stallion, and helps to physically prepare the mare for conception.

It generally occurs during the spring and summer months and is controlled by the length of the day. The cycle first triggered when the days begin to lengthen. The estrous cycle lasts about 19–22 days, with the average being 21 days.

As the days shorten, the mare returns to a period when she is not sexually receptive, known as anestrus.

Anestrus, occurring in the majority of mares, prevents the mare from conceiving in the winter months, as that would result in her foaling during the harshes part of the year, a time when it would be most difficult for the foal to survive.

This cycle contains 2 phases:

• Estrus, or Follicular, phase: 5–7 days in length, when the mare is sexually receptive to a stallion. Estrogen is secreted by the follicle. Ovulation occurs in the final 24–48 hours of estrus.

• Diestrus, or Luteal, phase: 14–15 days in length, the mare is not sexually receptive to the stallion. The corpus luteum secretes progesterone.

Depending on breed, on average, 16% of mares have double ovulations, allowing them to twin, though this does not affect the length of time of estrus or diestrus.

Effects on the reproductive system during the estrous cycle:

Changes in hormone levels can have great effects on the physical characteristics of the reproductive organs of the mare, thereby preparing, or preventing, her from conceiving.

• Uterus: increased levels of estrogen during estrus cause edema within the uterus, making it feel heavier, and the uterus loses its tone. This edema decreases following ovulation, and the muscular tone increases. High levels of progesterone do not cause edema within the uterus. The uterus becomes flaccid during anestrus.

• Cervix: the cervix starts to relax right before estrus occurs, with maximal relaxation around the time of ovulation. The secretions of the cervix increase. High progesterone levels (during diestrus) cause the cervix to close and become toned.

• Vagina: the portion of the vagina near the cervix becomes engorged with blood right before estrus. The vagina becomes relaxed and secretions increase.

• Vulva: relaxes right before estrus begins. Becomes dry, and closes more tightly, during diestrus.

Maternal recognition of pregnancy

In all large animal species, including the horse, the uterus must determine if a pregnancy is present or absent prior to the end of this normal luteal phase. The term for this process is ‘maternal recognition of pregnancy’.

The critical features of the recognition process are:

• The embryo produces a chemical signal

• The signal is detected by the dam’s uterus.

In the absence of an embryo or failure to detect an embryonic signal, the endometrial lining of the uterus releases hormones (prostaglandins) that travel through the blood stream to the ovary and destroy the corpus luteum. Progesterone levels drop rapidly and the mare will then develop another follicle and return to heat.

This cycle repeats itself multiple times each breeding season in the non-pregnant mare. In the presence of an embryo, the endometrium does not release significant amounts of prostaglandins into the circulation. The corpus luteum is thus preserved and production of progesterone is allowed to continue.

Progesterone is a key hormone required for maintenance of pregnancy and will also prevent the mare from returning to heat.

In some instances, the corpus luteum of a non-pregnant mare can continue to produce progesterone beyond the normal two-week lifespan and an affected mare will fail to return to estrus.

The term for persistence of progesterone production by a corpus luteum is phantom pregnancy.

Causes of Phantom Pregnancy

Causes of phantom pregnancy include embryonic loss after the time of maternal recognition of pregnancy, diestrous ovulations, severe uterine pathology, and potentially inadequate prostaglandin release.

The corpus luteum will be spared if a mare becomes pregnant and stays pregnant past the time of maternal recognition of pregnancy (days 12 to 14 post-ovulation). Mares that lose their pregnancy after the window of opportunity for maternal recognition will retain their corpus luteum.

In other words, mares have one chance per estrous cycle to determine their own pregnancy status and to ‘recycle’ themselves if they are not pregnant. Mares with severe, chronic damage to their uterine lining may have an increased incidence of persistence of the corpus luteum.

This is because the damaged endometrium may have a decreased ability to release sufficient prostaglandins to destroy the corpus luteum

False pregnancies are not uncommon in mares. The incidence may range from 5 to 10% of estrous cycles.

Mares that fail to return to estrus within 2 to 3 weeks after going out of heat are not always in foal. It is recommended that an ultrasound examination be performed 14 to 16 days after breeding to determine if a mare is pregnant and to detect the presence or absence of twins.

A recheck should be performed at 25 to 35 days to verify that the mare is still pregnant. Phantom pregnant mares will not return to heat as long as the corpus luteum is actively producing progesterone. The lifespan of a retained corpus luteum may be up to 2 to 3 months.

Consequences

Consequently, a persistent corpus luteum can have a serious adverse effect on the breeding season if the condition remains undiagnosed and untreated.

Veterinary examination of an affected mare will reveal good tone in the uterus and cervix on palpation and the presence of a corpus luteum during ultrasound evaluation of the ovaries.

The condition of phantom pregnancy is easy to treat if recognized.

Treatment

Administration of a single dose of prostaglandins will destroy the retained corpus luteum and the mare will return to estrus in 3 to 4 days.

However, it is critical that the mare be examined by ultrasound prior to administration of prostaglandins to confirm that the mare is not actually pregnant and that no other reproductive abnormalities are present. Inadvertent or inappropriate administration of prostaglandins to a pregnant mare will result in loss of the pregnancy

#pregnancy #mare