Uterine inertia is a failure of the doe’s expulsive efforts during
delivery. Contractions of the uterine muscle first lifts the fetus into the
pelvic inlet, then abdominal muscle contractions add more force to expel the
kids. A complex set of hormonal events directs all of this. Inertia may develop
during first or second stage labor, and there are two distinct forms. Primary
inertia is due to failure of the uterine muscle to work sufficiently due to a
variety of physical or hormonal reasons. Secondary inertia is the result of
dystocia or exhaustive labor.
Primary Uterine Inertia
Primary inertia is the most common of the two types in litter-bearing species. Degrees of inertia range from complete failure of the uterus to normal delivery with retained placenta. While it may be impossible to discover the true cause in some cases, knowing what to look for may be helpful.
Some breeds or strains may have an inherited weakness of the uterus. This may be mistaken for management problems, like females being overweight. A large litter or large kids may stretch the uterus excessively and interfere with its ability to contract.
In cattle, a condition called prolonged gestation can occur when the hormonal mechanism for starting delivery is absent. Pituitary gland aplasia (abnormal development) of calves has been found in some of these cases.
Fatty infiltration of the myometrium (uterine muscle) may cause slow or unproductive labor. Fat does are at high risk. Ketosis, a metabolic disease related to fat body condition, may combine with a fatty uterus to produce insufficient contractions. It is known that hormones involved in the delivery process work sluggishly in fat tissues, so fat mothers experience either delays in receiving these hormonal messages or have weakened response to them. Thin does may also develop ketosis, but for different reasons. A tendency toward ketosis and hypocalcemia, two metabolic diseases which occur at or near parturition, may be inherited or due to inappropriate nutrition during pregnancy. Hypocalcemia also interferes with the birth process. Both of these conditions must be treated immediately.
Stress interferes with hormone interaction near and during birth. Oxytocin is the pituitary hormone responsible for uterine contractions and the milk let-down response during nursing/miling. Epinephrine released by a stressed doe cancels the effects of oxytocin, and the doe is unable to contract. In slow or unproductive labor, ask yourself if the doe is nervous. Some does shut down labor when they are moved to different surroundings. If she does not calm down in a new location within an hour, return her to her usual habitat. Over-anxious owners who fuss and make noise are also very stressful to the doe in labor. Some does do not like a crowd watching them kid. Would you?
A doe may have sluggish labor for several other hormonal reasons. A single female fetus, abortion or premature birth may not contribute enough hormones to terminate the pregnancy normally. Abortions and premature deliveries may be caused by bacterial infections that debilitate the uterus. If you have more than one abortion per season, it is a good idea to have lab analysis of the fetus, placenta and the mother’s blood. Advanced age can result in inertia because the body operates less efficiently.
Uterine rupture and uterine torsion interrupt or prevent the uterus’ contractile ability. Rupture and torsion may occur up to several weeks before the due date or during the birth process. First stage labor is noticeable due to hormones, it fails to progress and cervical dilation will be incomplete. If a doe abruptly stops hard labor, uterine rupture is a possibility.
Even if the uterus is strong and does its job, weak abdominal muscles can hamper delivery. This is more of a factor in older does than younger ones.
If a doe remains in the first stage of labor and makes little or no effort to go into hard labor, a manual examination should be made to find out why.
Secondary Uterine Inertia
This is a direct result of dystocia. Futile efforts to pass a malpresented fetus cause the doe to cease her expulsive efforts. Some cases are due to exhaustion from prolonged, unproductive labor. Prevention is aimed at being on hand to recognize that labor is abnormal and giving assistance.
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