Mare Reproductive Loss Syndrome
Encyclopedia
Mare Reproductive Loss Syndrome (MRLS) has been diagnosed in mares of all breeds and ages. It was initially observed in Kentucky
in a three week period around the first of May, 2001, when about 20% to 30% of Kentucky's pregnant mares suffered abortions. The total economic loss to Kentucky and the racing industry for the 2001 MRLS season was estimated at $500 million.
, uveitis
and encephalitis
syndromes were identified.
During the three weeks around the first of May, 2001, about 20% to 30% of Kentucky's pregnant mares suffered abortions. Of foals conceived in spring 2001, about 2000 were lost, the so-called Early Fetal Losses (EFLs). Of foals conceived during the spring of 2000, and then close to term, at least 600 were lost, the so-called Late Fetal Losses (LFLs). Based on these overwhelming reproductive losses, the syndrome was named the Mare Reproductive Loss Syndrome (MRLS). The total economic loss to Kentucky and the racing industry for the 2001 MRLS season has been estimated at $500 million.
During the spring of 2001 Kentucky experienced an unusually heavy infestation of Eastern tent caterpillar
s. As part of an extensive and multifaceted investigation spearheaded by the University of Kentucky
, a rigorous epidemiological survey by Dr. Roberta Dwyer and her associates confirmed an association of MRLS with presence of the caterpillar. The exact mechanism by which the caterpillar caused MRLS is still under investigation. The condition was correlated spatially and temporally to the presence of Eastern tent caterpillars (ETCs), and ultimately linked to black cherry tree leaves,
Early and late fetal loss can be observed within the first and last trimester of pregnancy respectively. For Early Fetal Loss (EFL) clinical signs from the sick mares included puss-like discharge from the vulva, fetal membranes protruding from the vulva as the fetuses were located in either the vagina or vulva. One to three days prior to the EFL, several mares showed mild colic
symptoms, abdominal straining or low-grade fever
. Within a week of abortion, inspections indicated moderate to severe inflammation
within the uterine region. Performing ultrasounds reveal either dead fetuses or live fetuses with a slow heart rate and lethargic movements. All the fetuses, both alive and dead, were surrounded by a cloudy amniotic fluid.
Clinical signs for Late Fetal Loss (LFL) included explosive parturition, dystocia
, foaling while standing, the placenta separating prematurely and foals either stillborn
or born weak. The placenta was observed to carry a pale brown hue as opposed to its usual dark reddish brown color. The umbilical cord was thick, dull, yellowish and inflamed. The weak foals may be incapable of breathing on their own and require resuscitation. These foals were also observed to be dehydrated, hypothermic, having irregular heartbeat and respiration. The majority of the foals did not survive past four days.
One finding observed exclusively in the Mare Reproductive Loss Syndrome was the unilateral uveitis; within the first 12 hours, mares expressed inflammation
around the eye along with fluid accumulation on the cornea
, anterior and posterior chambers due to the inflammation. The fluid in the anterior chamber exhibits a tan yellow hue and often accompanied by haemorrhaging around the iris’ surface.
drugs.
Preventive measure can include cutting down cherry trees, spraying ETC nests with insecticides, and preventing the mares from eating on the pastures (muzzling them).
For more information see A Toxicological Investigation of Mare Reproductive Loss Syndrome
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
in a three week period around the first of May, 2001, when about 20% to 30% of Kentucky's pregnant mares suffered abortions. The total economic loss to Kentucky and the racing industry for the 2001 MRLS season was estimated at $500 million.
History
MRLS was first identified on April 26, 2001 by Dr. Thomas Riddle, who on that day observed an unusual number of equine in utero early fetal deaths in 60 day-old fetuses that he was ultrasound examining for sex determination. These early fetal losses were followed by a sequence of early and late fetal losses and, somewhat later, the coincident pericarditisPericarditis
Pericarditis is an inflammation of the pericardium . A characteristic chest pain is often present.The causes of pericarditis are varied, including viral infections of the pericardium, idiopathic causes, uremic pericarditis, bacterial infections of the precardium Pericarditis is an inflammation of...
, uveitis
Uveitis
Uveitis specifically refers to inflammation of the middle layer of the eye, termed the "uvea" but in common usage may refer to any inflammatory process involving the interior of the eye....
and encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
syndromes were identified.
During the three weeks around the first of May, 2001, about 20% to 30% of Kentucky's pregnant mares suffered abortions. Of foals conceived in spring 2001, about 2000 were lost, the so-called Early Fetal Losses (EFLs). Of foals conceived during the spring of 2000, and then close to term, at least 600 were lost, the so-called Late Fetal Losses (LFLs). Based on these overwhelming reproductive losses, the syndrome was named the Mare Reproductive Loss Syndrome (MRLS). The total economic loss to Kentucky and the racing industry for the 2001 MRLS season has been estimated at $500 million.
During the spring of 2001 Kentucky experienced an unusually heavy infestation of Eastern tent caterpillar
Eastern tent caterpillar
The Eastern tent caterpillar is a univoltine, social species that forms communal nests in the branches of trees. It is sometimes confused with the gypsy moth, or the fall webworm and may be erroneously referred to as a bagworm which is the common name applied to unrelated caterpillars in the...
s. As part of an extensive and multifaceted investigation spearheaded by the University of Kentucky
University of Kentucky
The University of Kentucky, also known as UK, is a public co-educational university and is one of the state's two land-grant universities, located in Lexington, Kentucky...
, a rigorous epidemiological survey by Dr. Roberta Dwyer and her associates confirmed an association of MRLS with presence of the caterpillar. The exact mechanism by which the caterpillar caused MRLS is still under investigation. The condition was correlated spatially and temporally to the presence of Eastern tent caterpillars (ETCs), and ultimately linked to black cherry tree leaves,
Clinical signs
The Mare Reproductive Loss Syndrome has been diagnosed in mares of all breeds and ages.Early and late fetal loss can be observed within the first and last trimester of pregnancy respectively. For Early Fetal Loss (EFL) clinical signs from the sick mares included puss-like discharge from the vulva, fetal membranes protruding from the vulva as the fetuses were located in either the vagina or vulva. One to three days prior to the EFL, several mares showed mild colic
Horse colic
Colic in horses is defined as abdominal pain, but it is a clinical sign rather than a diagnosis. The term colic can encompass all forms of gastrointestinal conditions which cause pain as well as other causes of abdominal pain not involving the gastrointestinal tract. The most common forms of colic...
symptoms, abdominal straining or low-grade fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
. Within a week of abortion, inspections indicated moderate to severe inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
within the uterine region. Performing ultrasounds reveal either dead fetuses or live fetuses with a slow heart rate and lethargic movements. All the fetuses, both alive and dead, were surrounded by a cloudy amniotic fluid.
Clinical signs for Late Fetal Loss (LFL) included explosive parturition, dystocia
Dystocia
Dystocia is an abnormal or difficult childbirth or labour. Approximately one fifth of human labours have dystocia.Dystocia may arise due to incoordinate uterine activity, abnormal fetal lie or presentation, absolute or relative cephalopelvic disproportion, or a massive fetal tumor such as a...
, foaling while standing, the placenta separating prematurely and foals either stillborn
Stillborn
Stillborn may refer to:*stillbirth in medicine*Stillborn , from Poland*"Stillborn" , a 2003 song by Black Label Society*Stillborn , a 1993 album by Malevolent Creation...
or born weak. The placenta was observed to carry a pale brown hue as opposed to its usual dark reddish brown color. The umbilical cord was thick, dull, yellowish and inflamed. The weak foals may be incapable of breathing on their own and require resuscitation. These foals were also observed to be dehydrated, hypothermic, having irregular heartbeat and respiration. The majority of the foals did not survive past four days.
One finding observed exclusively in the Mare Reproductive Loss Syndrome was the unilateral uveitis; within the first 12 hours, mares expressed inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
around the eye along with fluid accumulation on the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, anterior and posterior chambers due to the inflammation. The fluid in the anterior chamber exhibits a tan yellow hue and often accompanied by haemorrhaging around the iris’ surface.
Causes
One of the main agents that appear to induce MRLS is the presence of Eastern tent caterpillars (ETCs) which are present temporally and spatially with the MRLS abortions. One of the primary foods for ETCs are the back cherry tree leaves. An experimental study to prove the cause and effect relationship with ETCs and MRLS was confirmed when all mares exposed to ETCs (by being fed fresh black cherry tree leaves) aborted and none of the control mares had aborted.Prevention and Treatment
There appears to be no effective treatment for Mare Reproductive Loss Syndrome. Mares which aborted are treated with broad spectrum antibiotics to avoid bacterial infections. The foals born from mares infected with MRLS are given supportive care and supplied with medication to reduce inflammatory response and improve blood flow, but none of the treatments appear effective as the majority of the foals do not survive. Unilateral uvbetis where treated with antibiotics and anti-inflammatoryAnti-inflammatory
Anti-inflammatory refers to the property of a substance or treatment that reduces inflammation. Anti-inflammatory drugs make up about half of analgesics, remedying pain by reducing inflammation as opposed to opioids, which affect the central nervous system....
drugs.
Preventive measure can include cutting down cherry trees, spraying ETC nests with insecticides, and preventing the mares from eating on the pastures (muzzling them).
For more information see A Toxicological Investigation of Mare Reproductive Loss Syndrome