Horse Trust-Funded Research Finds IDO Protein May Help Maintain Equine Pregnancy, Prevent Fetal Loss

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An announcement received from the British-based charity The Horse Trust has been edited and expanded for an international audience. The Jurga Report is pleased to provide this exposure for The Trust and this news for horse breeders and reproduction specialist.

A research project funded by The Horse Trust in Great Britain has ascertained that the expression of a protein in horses is critical in maintaining pregnancy.

The research project was undertaken by Dr Lucy Woolford and was conducted at the Royal Veterinary College. Woolford is now Lecturer in Veterinary Pathology at the University of Adelaide, Australia.

In spite of advances in equine reproduction science, equine fetal loss continues to be a problem. Fetal loss caused by equine herpes virus often occurs in the last month of pregnancy. Photo courtesy of

In spite of advances in equine reproduction science, equine fetal loss continues to be a problem. Fetal loss caused by equine herpes virus often occurs in the last month of pregnancy. Photo courtesy of

Infertility and fetal loss are significant problems within the equine industry, and cause distress to both the owners and the mares. In around 20 percent of cases, the cause of fetal loss is unknown (Smith et al 2003).

The research, funded by The Horse Trust, aimed to learn more about how pregnancy is maintained in horses and how equine herpes virus (EHV), in particular, may trigger fetal loss.

Maintaining a viable pregnancy is dependent on the ability of the mare's immune system to "tolerate" the immunologically "foreign" fetus. The ways in which a mare tolerates the developing fetus is not fully understood, but in humans, primates and mice, a protein called indoleamine 2,3-dioxygenase (IDO) is produced by the pregnant uterus and has been shown to be important.

The research team looked for the presence of IDO and the expression of genes coding this protein in archive tissues of equine placentas by using immunochemistry and PCR. They found that IDO was expressed in the equine placenta between days 40 and 70 of gestation, correlating with early invasive stages of placental development in the mare. This finding suggests that expression of IDO in the equine placenta may help prevent immunological rejection of pregnancy, as it does in other animals.

The researchers also performed preliminary investigations into expression of IDO in equine herpes virus-1 (EHV-1) infected mares. A previous study found infection with equine herpes virus to be the cause of equine fetal loss in 6.5 percent of cases in the United Kingdom (Smith et al 2003). It is also a distressing cause of fetal loss, as abortions commonly occur in the last month of pregnancy (the gestation period in horses is 11 months).

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The researchers found strong expression of IDO in multiple uterine blood vessels of an EHV-1 infected mare that had aborted her fetus. This suggests that expression of IDO may be involved in viral abortion, however further research with a larger sample size is needed to determine the importance of this protein in equine herpes-viral abortion.

"We believe this research, which was funded by The Horse Trust, is the first study ever to describe the expression and localization of IDO in equine tissues," said lead researcher Woolford. "More research is needed to understand the immunology of pregnancy and how IDO might contribute to maintenance of pregnancy in mares. More research is also needed to further understand how equine herpes virus causes fetal loss."

Woolford's research has been submitted for publication in a veterinary journal. The research team also included Dr Sandra Schoeniger, Dr Amanda DeMestre, Professor William Allen and Professor Ken Smith.

Reference: Smith KC, Blunden AS, Whitwell KE, Dunn KA, Wales AD. A survey of equine abortion, stillbirth and neonatal death in the UK from 1988 to 1997. Equine Vet J. 2003 Jul;35(5):496-501.

About The Trust: The Horse Trust, founded in 1886, is the oldest horse charity in the UK. Based at Speen, Buckinghamshire, it provides a place of retreat for working horses that have served their country or community and nurtures them throughout their final years. The charity also gives sanctuary to horses, ponies and donkeys that have suffered and need special treatment. The Horse Trust funds non-invasive research that advances knowledge of equine diseases, improving diagnosis and treatment and reducing suffering among equines worldwide. The charity also offers training for professionals and owners, with a focus on equine welfare and quality of life assessment.

(Note from The Jurga Report: The Horse Trust was once known as The Horse for Rest for Horses. It has a long and illustrious history, and the little bio that The Trust provided with their press release is very modest. Their contributions to equine and veterinary science have been extraordinary and wide-ranging. Their steadfast mission of caring for horses in need has been exemplary and inspirational.)