We get a lot of
questions about female dogs having their menstrual periods. In fact,
the menstrual cycle is a primate phenomenon; dogs have an estrus
cycle that includes a period of false pregnancy. This false
pregnancy, or pseudocyesis, can get out of control, lasting for
weeks with the dog producing milk and sometimes mothering a soft
toy. So what should one do when this happens?
Before talking about
treatment, let’s explain the natural estrus cycle of the dog. The
female dog comes into season approximately every 6 to 8 months,
though this period becomes more erratic with age and is somewhat
irregular when cycles first begin. The exception to the every 6 to 8
months rule are African breeds (Basenji, Rhodesian Ridgeback) who
cycle once a year. When female dogs get older (say, age 7 or older)
they do not stop cycling; there is nothing similar to menopause.
The first phase of
the cycle is called proestrus and is characterized
by a swollen vulva, a bloody vaginal discharge, and attraction of
male dogs. She flirts with the male but will not allow him to mount.
The bloody vaginal discharge is what seems to lead to the
misconception that the dog is menstruating. In fact, the blood comes
directly from the walls of the vagina rather than the sloughing of
the uterine lining as occurs in menstruation.
The second phase of the cycle is called estrus,
which is characterized by the change in character of the vaginal
discharge from bloody to straw colored. At this time the female
begins to allow the male to mount. It is classically the change from
proestrus to estrus that ovulation occurs and the female is most
fertile.
After the mating and
the discharge is over, the period of diestrus
begins. The female is hormonally pregnant regardless of whether or
not she is actually pregnant. During this time progesterone is
produced by a structure in the ovary called a corpus luteum.
This structure is produced by ovulation when the ova (eggs) are
released. If the dog is pregnant, other hormones will take over to
maintain the corpus luteum for the entire 63 days of the pregnancy.
If she is not pregnant, the corpus luteum must simply wear out
before she goes back into the period of hormonal inactivity in which
she spends the bulk of her time. The corpus luteum wears out slowly
(rather than suddenly as in pregnancy and puppy birth) over 70 days
or longer. Remember, during this time her body essentially thinks
she is pregnant. All the hormones are present; only the puppies are
missing.
Clinical
False Pregnancy
When false pregnancy
persists it can be a nuisance. The female dog can show the following
signs:
• Nesting
• Mothering inanimate objects
• Lactating (giving milk)
• Abdominal distension
• She can even appear to go into labor
Some female dogs are
very sensitive to the hormonal fluctuations of the cycle. Diagnosis is
made by history and physical examination rather than by blood test. The
key is to find symptoms of pregnancy in a female dog that is not
pregnant. Symptoms generally become noticeable 6 to 12 weeks after
estrus.
Treatment
If symptoms are mild,
treatment is unnecessary as the condition resolves within 3 weeks. It
may be tempting to put warm compresses on the breasts or wrap them to
prevent milk leakage causing stains in the house. It is important to
remember that any touching of the mammary tissue is what stimulates milk
production, so it is important to minimize tactile stimulation. If the
female is licking herself, she may need an Elizabethan collar to
minimize stimulation.
If a more aggressive
approach is needed, a diuretic such as
furosemide can be prescribed. The idea is that mild dehydration will
end the lactation. Some people may want to try water deprivation but
this is potentially
dangerous and should not be attempted without specific veterinary
guidance.
If this doesn’t work,
hormonal medications can be used. Progesterone can be used but after
the course of medication is complete, the false pregnancy recurs so this
is not a good choice. Estrogens are also not a good choice as
they bring the dog back into estrus symptoms. A week’s course of the
male hormone mibolerone has generally been successful but the medication
is no longer available.
Hormones that inhibit
prolactin (the hormone of milk production) are currently the best
choices when medications are needed. Bromocriptine can
be obtained from a compounding pharmacy and given until lactation ceases
(about a week or two) but tends to cause upset stomach.
Cabergoline has fewer side effects but is given similarly and
tends to be more expensive. Both these medications will cause abortion
if the dog actually turns out to be pregnant so it is important to be
sure.
Spay During
False Pregnancy?
It might seem like a
good idea to spay the female to end the false pregnancy as spaying will
remove the ovaries and the corpora lutea they carry. Unfortunately, this
does not end the prolactin production from the pituitary gland so
spaying may actually prolong the false pregnancy. It is best to wait
until the false pregnancy is over and then spay her to prevent future
episodes.
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