Page 496 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 471

VetBooks.ir Prognosis • Placentitis.
• Abnormalities in oxytocin release.
The prognosis for the foal born following premature
placental separation can vary from guarded to grave
depending on the cause and degree of placental dam- The incidence of retained fetal membranes in one
age prior to parturition and the rapidity of response survey was suggested to be 2–10% of all parturitions,
to the abnormal delivery. Following this condition, with a higher incidence in draught or cold-blooded
many foals are born with considerable problems and mares, older multiparous mares and mares that had
require extensive and costly treatment to survive. previously suffered from the condition. Retention of
fetal membranes usually involves the tips of the uter-
RETAINED FETAL MEMBRANES ine horns, more often in the non-gravid horn than
(PLACENTA) the gravid horn. The exact mechanism that causes
interference with the normal separation process is at
Definition/overview present unknown.
Retained fetal membranes are a common complication Complications that follow placental retention
of the post-partum mare. In normal circumstances are more common in larger, heavy mares and are
the placenta is passed from the uterus within 1–3 associated with bacterial proliferation in the uterus
hours of birth (third stage of parturition), although and a buildup of autolytic enzymes. In addition to
there is considerable variation in normality and some endometritis and metritis in the uterus, this bacte-
mares will retain it for significant periods without rial and enzyme mix may be absorbed systemically
short- or long-term complications. Retention of fetal and lead to a bacteraemia/septicaemia and endotox-
membranes has a multifactorial aetiology, probably aemia, with a high incidence of severe, acute lamini-
leading to abnormalities of uterine motility and/or tis. Retained fetal membranes may also predispose to
maturational processes within the microcotyledons. uterine prolapse (p. 467).
In some mares, especially the larger heavy, draught
types, serious complications related to the metritis– Clinical presentation
laminitis–septicaemia complex have been recorded. The retained fetal membranes are often observed
Treatment is aimed at encouraging release of the hanging from the vulval lips, with the amnion most
fetal membranes and prevention of secondary com- visible outside. By definition, any mare with the
plications. The prognosis is fair in cases treated early fetal membranes still visible after 3–5 hours post
and aggressively, but poor in advanced chronic cases. partum has a retention, but there is considerable
variation across breeds and types. If the mare is still
Aetiology/pathophysiology in the third stage of parturition (experiencing uter-
Causes of retained fetal membranes include any ine contractions), she will show signs of abdominal
factor or condition that affects uterine motility, discomfort and may well pass the fetal membranes
although it does occur following what appear clini- fairly quickly. If they are truly retained, then no
cally to be normal deliveries: discomfort is usually apparent. The mare should
receive a full physical examination to detect any of
• Dystocia, especially after extensive the common complications of retention of the fetal
manipulations or embryotomy. membranes.
• Induced parturition.
• Premature delivery. Diagnosis
• Abortion. Clinical signs are diagnostic. If the mare develops
• Caesarean section. any of the complications, bacterial samples for cul-
• Deficiencies and imbalances in selenium and ture and sensitivity from the uterus and blood should
calcium/phosphorus. be taken, along with blood samples for a full hae-
• Uterine inertia/fatigue (e.g. post hydrops or matology and biochemistry analysis. Subsequently,
twin pregnancy, inadequate exercise or obesity, lateral foot radiographs may be useful in the man-
general anaesthetic). agement of any laminitis. All fetal membranes