Hydrops is the result of a malfunction of the uterus or placenta, causing an increased production and accumulation of fluid in the amnionic sac (Hydrops amnion) or the allantoic sac (hydrallantois).
Hydrallantois is by far the more common condition, and is primarily the result of dysfunction of the placenta, resulting in an increased production of a fluid closely resembling blood plasma within the allantoic sac. This condition commonly occurs during a 5-20 day window during the third trimester of pregnancy. Commonly a decreased number of uterine attachment sites are noticed, and those that are present are larger than normal in an attempt to compensate for the decreased surface area. Most cows with hydroallantois are noted to have decreased estrogen levels, although it is unknown what role this plays in the disease. Fluid accumulation can reach volumes of 150-250 liters, and the symptoms noted are highly variable in accordance with the amount of fluid present. Mild cases are commonly unnoticed, and spontaneously resolve. More severe cases may result in a significant abdominal distention on both the right and left sides causing discomfort, decreased appetite, and reluctance to move. In these more severe cases, increased heart rate, anorexia, and dehydration should be anticipated, as ketosis and recumbency are potential complications. In rare cases, the prepubic tendon may rupture under the weight of the fluid and fetus, resulting in an untreatable dropped abdomen.
A less common occurrence, hydramnios results from an abnormality of the fetus, which causes the gradual accumulation of fluid within the amniotic sac immediately surrounding the fetus. During normal pregnancy, amniotic fluid is swallowed by the fetus, then absorbed, however if the fetus is abnormal, this mechanism does not occur, and the fluid accumulates. Fetal abnormalities causing this defect include bulldog calves (Dexter cattle), brachygnathic calves, muscle contracture monsters, pituitary hypoplasia/aplasia, and hydrocephalic calves.
On rectal palpation, hydroallantois will palpate as a fluid filled uterus with failure to appreciate the placentomes or fetus. In both conditions, ultrasound can be utilized to asses fetal heart-rate and viability.
Salvage for slaughter is generally high on the list of options for both conditions, as hydrops risks the viability of both the fetus and cow. As hydroallantois is a placental disease, reoccurrence is likely. Even if the fetus can be brought to term, the dam should be culled. If the disease is severe enough to cause recumbency or rupture of the prepubic tendon, euthanasia should be immediately pursued. In dairy cattle, if the pregnancy is terminated it is unlikely that the cow will have a productive milk cycle, and thus is may not be economical to keep her through the next lactation. If the cow is within 2-3 weeks of pregnancy, and the fetus is considered valuable, it may be feasible to take the pregnancy to term.
If treatment is to be pursued, the two options are elective c-section and induction of parturition. Many clinicians feel that better results are obtained with induction, however this should be decided on a case-by-case basis. For example, if a fetal structural abnormality exists that would prevent passage through the vaginal canal, c-section should be elected. Induction of parturition can be achieved with 25-35mg of prostaglandin F2α either alone or with dexamethasone. This protocol should induce the cow within 24-48 hours. The majority of calves are non-viable, but if the calf is alive, the dam rarely has normal colostrum, requiring the use of frozen or replacement colostrum. Plasma transfusion for the calf may be considered, as many of these calves have premature closure of the gut, and thus cannot absorb the antibodies in the colostrum.
The prognosis for future fertility of the dam is much improved for hydramnion, which is a defect in the fetus, versus hydroallantois, which is the result of a uterine abnormality. Both conditions may result in retained fetal membranes and metritis, particularly if parturition was induced, and prophylactic antibiotics may be warranted.
M. Vandeplassche, R. Bouters, J. Spincemaille and P. Bonte. Induction of parturition in cases of pathological gestation in cattle. Theriogenology Volume 1, Issue 3, March 1974, Pages 115-121.
Youngquist, RS and Threlfall, WR. Current Therapy in Large Animal Theriogenology. Saunders Elsevier Publishing, St. Louis, MO. 2007.
Kenneth L Marcella. Hydrops rare, but know signs. DVM Magazine, Mar 1, 2002 Click here to see full article http://126.96.36.199/library/article/hydrops-rare-known-signs