Equine abortion is defined as pregnancy loss prior to 300 days of gestation, whereas fetuses dying after 300 days are classified as stillbirths (Acland 1993]. There have been several surveys of the causes of equine abortion in the UK (Piatt 1973; Whitwell 1980; Smith et al. 2003]. This review is based on the most recent survey, which concerned the diagnoses for 1252 equine fetuses and neonatal foals examined at the Animal Health Trust in Newmarket during 1988-1997, together with some more recent observations.The most common cause of abortion in the Newmarket survey was umbilical cord torsion (38.8% of cases]. This diagnosis was most common in mid-gestation and was associated with vascular compromise in the umbilical cord, which was oedematous, congested or haemorrhagic with variable dilation of the urachus. Fetal death generally occurred in utero. Extreme umbilical cord length is the principal risk factor for this condition (Whitwell 1975].
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