The 2005). This third type of prolonged gestation in

The differential diagnosis in cases of prolonged
gestation

in cattle consists of three
major elements. First and most

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

commonly, human error, such as miscalculation of
the prospective calving date or failure to record a subsequent service is
involved, leading to an incorrect diagnosis of prolonged gestation (Jackson
2005). Double checking the breeding records, eliminating all possibilities of a
subsequent service and a good rectal examination (palpation and/or ultrasonography)
to estimate the fetal age is mandatory before taking other possible causes into
consideration. Secondly, intrauterine death and fetal mummification can also
result in indefinite continuation of the pregnancy. These dams do not show
abdominal enlargement as expected in late pregnancy. A dead fetal mass without
fetal fluids can be palpated in an irregularly shaped, contracted uterus
(Jackson 2005).True prolonged gestation of a living fetus is relatively rare
and is due to a defective hypothalamic-pituitary-adrenal axis (Jackson 2005).
This third type of prolonged gestation in cattle is sometimes associated with a
primary adrenal insufficiency (Stabenfeldt and others 1975) or, more commonly,
with defects of the brain in general and of the pituitary gland in particular.

Infectious, toxic and genetic causes have been
associated with brain or pituitary defects, resulting in prolonged gestations
in cattle (Hanzen 2005). Bovine viral diarrhoea, Akabane or bluetongue virus
infections can cause severe brain damage in the fetus, including anencephaly,
hydrencephaly or porencephaly, resulting in rupture of the hypothalamus and/or
hypophysis (Hanzen 2005, Jackson 2005). Ingestion of Veratrum californicum or
Veratrum album has also been associated with prolonged gestation due to severe
cranial deformities and brain defects in the bovine fetus (Jackson 2005).Cases
of primary hypophyseal anomalies and prolonged gestation with a possible
genetic background have been reported in different cattle breeds such as
Ayrshire (Wilson and Young 1958), German Fleckvieh (Hafner and others 1991),
Guernsey (McEntee and others 1952, Kennedy and others 1957), Holstein-Friesian
(Graves and others 1991), Jersey (Blood and others 1957) and Meuse-Rhine-Yssel
(Matthijsen and Borst 1983); gestational lengths of up to 469 days have been
reported (Hafner and others 1991). In Holstein-Friesian cows, hypophyseal
hypoplasia has been identified as resulting from an autosomal recessive gene
defect (Jackson 2005). In the Holstein-Friesian, Ayrshire and Guernsey breeds,
adeno-hypophyseal hypoplasia is associated with fetal gigantism, hirsutism,
retarded ossification and hypoplasia of the thyroid and adrenal glands. Another
autosomal recessive genetic defect resulting in prolonged gestation has been
described in Guernsey and red-white Swedish cattle, and is associated with
hydrencephaly, fetal growth retardation, delayed ossification, hypotrichosis
and atresia jejunalis (Hanzen 2005)

In a case of suspected prolonged gestation, the dam’s
breeding records, if available, should be checked to ensure that parturition
truly is overdue. Treatment of a case in which gestation is not genuinely
prolonged may result in the delivery of a premature fetus that is unlikely
to survive. Once the true length of gestation is established, a full clinical
examination of the dam should be conducted. In cattle; rectal examination of
the uterus and its contents is an important diagnostic aid. Fetal parts may be
palpable, and in some cases it is possible to detect an abnormal cranium. An
ultrasonographic scan may confirm the presence of fetal abnormalities,
including a thin-walled, fluid-filled cranium. The weight of an overdue fetus
may cause it to pass under the rumen while still within the uterus, so that it
cannot be palpated per rectum. In some animals, prolonged gestation is
accompanied by development of excessive amounts of fetal fluid. The origin of
excessive fetal fluid can be assessed by analysis of sodium and chloride levels
in an aspirated sample. Amniotic fluid contains sodium at ~120 mmol/L and
chloride at ~90 mmol/L. Allantoic fluid contains sodium at 50 mmol/L and
chloride at 20 mmol/L. The correlation between hydrops amnion and hydrops
allantois and prolonged gestation is tenuous, however. Most fetal giants suffer
from oligoamnios.In true prolonged gestation; the fetus is unlikely to be
of any economic value. Treatment should be aimed at fetal delivery with minimal
damage to the dam. In cases of fetal giantism, the dam may be distressed by the
weight of the fetus and its associated fluids. Painful edema in front of the
udder may indicate rupture or impending rupture of the prepubic tendon. A
canvas sling support can be placed around the abdomen to prevent further damage
until the pregnancy is terminated. General health of the dam should be assessed
and economic considerations discussed with the owner before treatment is
attempted. Milk production may be compromised. Successful induction of
parturition requires an intact fetal hypothalamic-pituitary-adrenal axis.
Pregnancy is maintained in cases of prolonged gestation chiefly by continued
production of progesterone by
the corpus luteum. Spontaneous induction of birth in cases of prolonged
gestation fails as a result of insufficient production of fetal cortisol and
the failure of luteolysis to occur. Birth in both cows and sheep can be
successfully induced by administering both prostaglandin F2? (and
its synthetic analogue cloprostenol) and the corticosteroid dexamethasone by IM injection. Luteolysis
is induced by the prostaglandin, and the maternal hormone cascade that
precedes parturition is initiated by the corticosteroid. In cows, 500 mcg
cloprostenol and 20 mg dexamethasone are
given; in sheep 125 mcg cloprostenol and 16 mg dexamethasone are recommended. A single dose
of these two drugs is normally effective. Parturition should begin in 24–72 hr.
Induced parturition should be monitored carefully. Assistance may be required
if there is evidence of uterine inertia or damage to the abdominal wall, either
of which might make expulsive efforts ineffective. Fetal malposition requiring
obstetric assistance may occur once birth begins. If the fetus is very
large, dystocia due to fetal-pelvic disproportion may occur, and assisted
delivery by careful traction may be attempted. If this is not possible,
cesarean section may be required. If the dam is seriously ill but considered
well enough to withstand surgery, an elective cesarean without an attempt at
vaginal delivery may be considered. Fetal dysmaturity can be a problem,
especially in very valuable cloned offspring, and intensive care facilities may
be needed. After fetal delivery, uterine involution may be encouraged by
administration of oxytocin. Fluid
therapy, antibiotics, and treatment with NSAIDs such as flunixin meglumine may
aid recovery and provide analgesia.