Katherine E. Whitwell

Twinning as a cause of foetal and neonatal loss in the Thoroughbred mare

Abstract A series of 62 sets of twins and their placentae were examined from Thoroughbred mares. All were considered to be bicornual pregnancies and dizygous. The majority (64·5 per cent.) of these pregnancies terminated in abortion or stillbirth of both twins from 3 months gestation to term, although most foetuses (72·6 per cent.) were slipped from 8 months to term. In the remaining cases either one (21·0 per cent.) or both twins (14·5 per cent.) were born alive. Foals at term were stunted and emaciated, and of the 31 foals alive at birth only 18 survived to 2 weeks of age. Twin placentae were divided into three morphological groups according to the disposition of the chorionic sacs within the uterus. Type A was seen in 79 per cent. of cases. The chorion of the larger twin occupied all of one horn of the uterus and most of the body, leaving the smaller twin only a small portion of the body and the other horn. These pregnancies frequently ended in abortion or stillbirth of one, or both twins. The larger twin had a much greater chance of survival than the smaller one. Type B occurred in 11 per cent. of cases. The villous surface areas was more or less equally divided, so that each foetus occupied one horn and half of the body. Both twins were usually born alive. Type C was seen in 10 per cent. of cases. Here there was much greater disparity between the surface areas of the 2 chorions. The smaller twin, occupying only part of one horn, died early on and became mummified. The larger twin was usually born alive and had a fair chance of survival. The loss of twin foetuses and the poor survival rates was attributed chiefly to placental insufficiency. The combined foetal surface area of the chorions of both twins was only slightly larger than that for a normal singleton foal. The presence of small vascular anastomoses was seen in many cases across the area that the 2 chorions were in contact. In some instances a chronic inflammatory reaction was seen in this area and it is suggested that this might be the result of an immunological reaction between the tissues of 2 foetuses.

A survey of equine abortion, stillbirth and neonatal death in the UK from 1988 to 1997.

REASONS FOR PERFORMING STUDY A detailed review of laboratory records for equine abortion is fundamental in establishing current disease trends and suggesting problems important for further research. OBJECTIVES To review the causes of abortion and neonatal death in equine diagnostic submissions to the Animal Health Trust over a 10 year period. METHODS The diagnoses in 1252 equine fetuses and neonatal foals were reviewed and analysed into categories. RESULTS Problems associated with the umbilical cord, comprising umbilical cord torsion and the long cord/cervical pole ischaemia disorder, were the most common diagnoses (38.8%: 35.7% umbilical cord torsion and 3.1% long cord/cervical pole ischaemia disorder). Other noninfective causes of abortion or neonatal death included twinning (6.0%), intrapartum stillbirth (13.7%) and placentitis, associated with infection (9.8%). E. coli and Streptococcus zooepidemicus were the most common bacteria isolated. Neonatal infections not associated with placentitis accounted for 3.2% of incidents; and infections with EHV-1 or EHV-4 for 6.5%. CONCLUSIONS Definitive diagnosis of equine abortion is possible in the majority of cases where the whole fetus and placenta are submitted for examination. POTENTIAL RELEVANCE Given the high incidence of umbilical cord torsion and related problems as causes of abortion in UK broodmares, more research on factors determining umbilical cord length and risk of torsion is essential.

Equine herpesvirus-1 abortion: atypical cases with lesions largely or wholly restricted to the placenta

Equine herpesvirus-1 (EHV-1) abortion is diagnosed by detailed examination of the aborted fetus, using a combination of gross findings, histopathology, virus isolation, polymerase chain reaction (PCR) and immunostaining. Conventionally, these tests are applied to selected target organs, particularly liver, lung, thymus and spleen (review; Allen et al. 1999). The macroscopic and microscopic lesions in the fetus are well described (Westerfield and Dimock 1946). A feature of spontaneous EHV-1 abortions in mares is the often sudden and explosive nature of the event, the fetus being expelled without warning and still enveloped within the fetal membranes. Experimental studies carried out in ponies in the early 1990s (Smith et al. 1992, 1993) gave the opportunity to investigate the histological events taking place within the uterus of mares aborting following EHV-1 infection. A number of recently infected mares aborted virologically negative fetuses, and it was possible to confirm that these abortions were associated with virus-related thromboses and endometrial infarction, which had apparently precipitated a cascade of events leading to wholesale premature placental separation from the endometrium and expulsion of the fetus and placenta. These findings initiated concerns as to whether, in some spontaneous abortions, similar events might occur, giving rise to false negative diagnoses if only fetal tissues were screened for virus. This paper, based upon experiences in diagnostic pathology, describes data that provide strong support for this hypothesis.

Clinical and pathological observations on generalized steatitis in foals

Abstract A form of generalized fat necrosis and steatitis occurs in pony and donkey foals. The clinical and pathological features of this disorder are described and its possible relationship to a similar condition in the Thoroughbred foal, and to yellow Fat Disease in other species, is discussed.

Systemic infection by equid herpesvirus-1 in a Grevy's zebra stallion (Equus grevyi) with particular reference to genital pathology.

A severe multi-systemic form of equid herpesvirus-1 infection is described in an adult zebra stallion. There was multifocal necrotizing rhinitis, marked hydrothorax and pulmonary oedema, with viral antigen expression in degenerating epithelial cells, local endothelial cells and intravascular leucocytes of the nasal mucosa and lung. Specific localization of EHV-1 infection was seen in the testes and epididymides, including infection of Leydig cells and germinal epithelium, which would have facilitated venereal shedding of virus in life. The case provided a unique opportunity to study hitherto undescribed aspects of the pathogenesis of naturally occurring EHV-1 infection in the male equine genital tract. Restriction digests of the isolate demonstrated a pattern similar to that of EHV-1 isolates previously recovered from aborted zebra and onager fetuses.

Two cases of equine pregnancy loss associated with Leptospira infection in England

INFECTION with Leptospira can cause abortions and stillbirths in domestic cattle, sheep and pigs, as well as in wild animals. It has also been well documented as a cause of abortions in mares in several countries, including the USA, Canada, South America, New Zealand, Australia and some European