Monitoring and Recommendations for the Prevention of Mare Reproductive Loss Syndrome (MRLS)
This is a working document that will be subject to change as further data are collected and analyzed. Updated recommendations will be posted at the Web site www.ca.uky.edu.
At the end of April 2001, veterinarians reported a disease outbreak, subsequently referred to as Mare Reproductive Loss Syndrome (MRLS), occurring among pregnant mares of all breeds in central Kentucky. Clinical signs of the disease during April and May included early and late fetal losses, the birth of weak foals, and a very small number of horses of different sexes and ages that exhibited pericarditis and unilateral uveitis. Infectious or contagious disease agents are not considered a primary cause, but environmental toxic agents remain the primary suspect. The exact cause or mechanism of the 2001 Mare Reproductive Loss Syndrome (MRLS) therefore remains unsolved. Epidemiological surveys have refined the risk factors, and studies on mechanisms continue.
The University of Kentucky College of Agriculture will establish a monitoring system to follow critical pasture and weather parameters in the spring of 2002. Environmental monitoring will alert owners and managers to avoid any potential risks during the next breeding season while furthering our understanding of the causes of MRLS. Horse farm owners and managers can and should implement procedures to reduce the risk of MRLS in 2002.
This document describes a proposed monitoring plan and contingency recommendations for managing the risk of MRLS. All University of Kentucky College of Agriculture publications cited in this document are available at our Web site at www.ca.uky.edu or from your local University of Kentucky Cooperative Extension Service office.
I. Monitoring Plans
These plans are the responsibility of personnel listed in "Section IIIPersonnel."
1. Location and Frequency of Sampling
Approximately 12 farms will be identified as sources of animal and plant data in the spring of 2002. The number of mares per farm to be monitored will range from 15 to 25. Those participating will include both high-risk and low-risk Thoroughbred and Standardbred farms in an area covering Fayette, Bourbon, Jessamine, and Woodford counties as defined by the incidence of MRLS in 2001. Farms will be sampled every two weeks from March 1 to June 30.
2. Reporting Frequency
General reports will be issued monthly through an oversight committee (specified under "Section IIIPersonnel" on page 10). If abnormal results are identified from monitoring of samples or if MRLS symptoms are observed, an alert notice will be issued with approval of the oversight committee as soon as results become available. It is recognized that cases may be reported outside of the farms selected for monitoring. Information will be posted on the College of Agriculture Web site at www.ca.uky.edu and distributed to various organizations representing the equine industry of Kentucky.
3. Farm and Equine Data
a. Animal data: Identify mares, breeding date, and reproductive status. Record any unusual clinical signs, e.g., fever and colic. Farms are to keep horse populations stable within test fields as much as possible or alert the University of Kentucky of the change at the next visit.
b. Field management history (e.g., fertilizer, lime application, herbicide application, removal of cherry or crab apple trees).
c. Pasture diagrams indicating major landmarks and other features (e.g., gates, waterers, streams, ponds, waterfowl, wild cherry trees, or crab apple trees).
d. Botanical description of pasture species and weeds present. This information should be updated weekly and recorded. Special notice of poisonous plants will be noted, especially hemlock.
e. Field diagram should indicate the general area from which samples were taken.
4. Environmental Monitoring
a. Fusarium mycotoxin, in and out of proximity to wild cherry trees, composite sample of many sites of the representative forage and weeds present. Kyle Newman, Venture Laboratories, Inc., Lexington
b. Ergot-type and loline alkaloids, in and out of proximity to wild cherry trees, composite sample of many sites of the representative forage and weeds present. Lowell Bush, University of Kentucky Department of Agronomy
c. Ergot-type and loline alkaloids, tall fescue only, composite sample from field. Lowell Bush, University of Kentucky Department of Agronomy
d. Cyanide, white clover, composite sample of many sites. Jim Crutchfield, University of Kentucky Department of Agronomy
e. Nitrates, composite sample of many sites of the representative forage and weeds present. Jim Crutchfield, University of Kentucky Department of Agronomy
f. Soil samples, in and out of proximity to wild cherry trees, composite sample of many sites. Kyle Newman, Venture Laboratories, Inc., Lexington
g. Weather data plus mold and spore counts. Tom Priddy, University of Kentucky Department of Biosystems and Agricultural Engineering
h. Cyanide-related parameters associated with the Eastern Tent Caterpillar
(ETC) (in wild cherry leaves, in caterpillars, in droppings from trees,
Special note: An aliquot of all samples will be frozen and stored.
5. Animal Monitoring
a. In the case of early fetal loss, the fetus if presented should be submitted to the Livestock Disease Diagnostic Center (LDDC). Blood and urine samples should be drawn and an endometrial swab obtained.
b. In the case of late fetal loss, the fetus should be delivered to the LDDC, blood and urine samples drawn from the mare, and an endometrial swab obtained.
c. Uterine biopsies following early and late fetal losses should be performed at the discretion of the attending veterinarian. Biopsies at 24 to 48 hours and 15 to 30 days post-abortion are requested and should be submitted to the LDDC.
d. If possible from cases of both early and late fetal loss, a sample of allantoic/amniotic fluid should be obtained and submitted to the LDDC.
e. In the case of weak foals sent to a clinic, a record of clinical evaluation as well as a hematological and biochemical profile should be kept and a blood and urine sample obtained from both the mare and foal and stored at -70°C.
f. A subset of the monitored farms will be selected for the collection of routine blood, urine, and other samples from at least 10 mares per farm every two weeks. This subset will include four high-risk and two low-risk farms. Farm veterinarians will draw blood serum (20 ml) and urine (100 ml) to be submitted to the LDDC. The blood will be spun and the serum and urine stored at -70°C.
g. All tissue and other samples stored at the LDDC will be subject to a range of testing procedures to be determined by pathologists at the LDDC.
II. Farm Contingency Plans
The University of Kentucky College of Agriculture recommends that farms consider the following contingency measures to reduce the risk of MRLS in 2002. These measures are indicated by the epidemiological studies and farm visits and are based on the best information available at this time. The decision to implement any or all of these measures should be based on the recognition that the risk factors for MRLS are multifaceted and that the onset was associated with abnormal weather conditions and the presence of unusually large numbers of the Eastern Tent Caterpillar (ETC) in 2001. Elimination of all risk factors may not be feasible on many farms. Implementation of all measures should be evaluated in light of individual farm conditions and all updated information as it becomes available.
Primary Preventative Measures
1. Minimize or eliminate exposure of pregnant mares to the Eastern Tent Caterpillar (ETC).
The epidemiological survey results and farm visits have found a high correlation between the presence of the ETC and host trees (cherry, ornamental fruit trees such as crab apple) and the occurrence of MRLS. Counts of egg masses indicate that ETC populations in 2002 will be high. Detailed recommendations are contained in the Cooperative Extension Service fact sheet titled Farm Contingency Plan for MRLS Risk Reduction for Kentucky Horse Farms Eastern Tent Caterpillar Recommendations--2002.
2. Keep pregnant horses out of proximity to wild cherry trees.
The link between wild cherry trees and MRLS is circumstantial and is yet unproven. However, in light of the strong correlation with MRLS and the known danger of cyanide poisoning from wilted leaves from fallen limbs, minimizing exposure is good management. Detailed recommendations are contained in the Cooperative Extension Service fact sheet FORFS 01-04 titled Removal of Fencerow Black Cherry.
3. Frequently clip pastures used by pregnant mares.
Mowing frequently will minimize seedheads and will ensure new vegetative growth in pastures. Field-by-field farm visits did find that mowing appeared to reduce MRLS in 2001, although this was not identified in the epidemiological survey.
4. Offer hay to horses on pasture.
This management practice was associated with a lower incidence of MRLS, according to the epidemiological survey.
These measures were not indicated by the epidemiological survey but are practices to consider. These and other measures may become important as more information becomes available.
1. Increase the grass-to-clover ratio in pastures.
A common factor identified during visits to farms experiencing losses was the presence of higher than average amounts of white clover. It is recommended therefore to increase the proportion and vigor of grass in the pasture by overdrilling grass seed and applying nitrogen fertilizer in the late fall. White clover can be minimized by herbicide application. It must be emphasized that this is not a recommendation to remove all white clover from pastures.
2. Restrict time on pasture when a hard freeze is expected following a warm period.
The onset of MRLS in 2001 was coincidental with a record warming period in early April, with a frost on April 17-18 followed by a strong warming trend. Additional weather stress occurred during April due to the drought conditions. The weather data will be closely monitored to see if the 2001 pattern is repeated, and "alerts" will be issued when appropriate.
3. Reduce exposure of pregnant mares to endophyte-infected tall fescue.
Although this factor was not correlated to MRLS and fetal losses, this is a prudent management practice in any year. Detailed recommendations are contained in the Cooperative Extension Service fact sheet ID-144 titled Understanding Endophyte-Infected Tall Fescue and Its Effect on Broodmares.
1. Mycotoxin binders have been fed by some farms.
Mycotoxin binders may be beneficial if mycotoxins are involved in MRLS. The decision to feed these products should be based on discussions between the farm manager and his or her nutritional advisors.
2. Mineral imbalance.
It has been suggested that MRLS may be associated with an imbalance of mineral intake, although further evidence is needed to support this hypothesis. As with No. 1 above, it is recommended that farms discuss with their nutritional and veterinary advisors the merits of mineral supplementation.
An oversight committee will be named to ensure efficient functioning of the monitoring process, approve changes, and facilitate communication. This committee is proposed to be composed of three veterinarians, two farm managers, two University of Kentucky faculty, and one or two representatives from the Kentucky Department of Agriculture.
The day-to-day responsibility for the monitoring program will be vested in a senior faculty coordinator from the College of Agriculture who shall be a member of the oversight committee.
The sampling program will be conducted using a scout supervisor and others as follows:
1. Scout Supervisor: Full-time postdoctoral scientist or Research Specialist.
a. Work closely with the faculty coordinator.
b. Train, supervise, and coordinate the sampling activities of field scouts.
c. Oversee sample handling and distribution to appropriate laboratories.
d. Facilitate and oversee data recording, analysis, and reporting.
2. Three seniors, graduate students, or interns.
a. Sample horse farms as directed by the scout supervisor.
b. Prepare and distribute samples to appropriate laboratories.
c. Aid in data entry, analysis, and reporting.
3. Administrative Assistant.
a. Aid in communication with horse farms, field personnel, and faculty.
IV. Approximate Costs