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June 20, 2002

Report from Dr. Roberta Dwyer
Department of Veterinary Science
University of Kentucky College of Agriculture

Farm Survey Results

As reported June 11, 2002, 92 Kentucky Thoroughbred farm managers responded to a questionnaire to estimate the 2002 early fetal losses (EFL).  Based on data provided, 92.3% of mares on these farms bred prior to April 1, 2002 were still pregnant as of June 1.  Farm mare populations ranged in size from 2-300 mares bred as of June 1, 2002 with an average size of 53 broodmares.

Of the responding farms, for 2001, 75 had EFL; 14 had no EFL; and 3 did not answer.  For 2002, 33 farms had EFL consistent with MRLS; 55 had no EFL; and 4 did not answer.  Of the 33 farms with EFL this year, 22 (67%) had lower losses than 2001; 7 had equal amount of losses; 3 had higher losses and 1 did not answer.

Eastern Tent Caterpillar (ETC) Control Measures

Managers were asked about the types of caterpillar control measures used on the farm this year with the following answers (most utilized more than one technique):
Spraying trees with Bt, Sevin, other chemicals
Keeping mares stalled during frost warnings
Keeping mares stalled at night
Eliminating cherry or crabapple trees
Limiting mare’s pasture exposure (daytime)
Manual removal of ETC eggs or tents
Tree injection to make leaves toxic to ETC

The majority of farms implemented between 2 and 5 control measures.  This shows the extensive efforts made by farms in controlling the ETC concentration on farms, as each of the ETC control techniques is labor intensive and costly.

A comparison was made between the number of measures used by farms having EFL in 2001 and 2002 versus farms having EFL in 2001 but not 2002.  Farms having EFL in both years used an average of 3.1 control measures; farms not having EFL in 2002 (but did in 2001) used an average of 3.4 control measures.  There was a trend in usage of more techniques on farms that did not have EFL in 2002 but did have problems in 2001.  This must be interpreted with the knowledge that the majority of farms with EFL in 2002 had a lowered incidence of the disease.

No individual technique was identified that made a significant difference between whether farms had EFL in 2002 or not.  A set of carefully controlled and highly expensive experiments would be needed to evaluate individual control measures.

Location of EFL Mares on Farms

For the 33 farms which had EFL in 2002, 25 (78.1%) had losses in mares housed primarily on the periphery of the farm, whereas only 2 had losses in centrally located paddocks and 5 farms had losses in both areas (1 survey had no response).

Of the 25 farms managers reporting losses primarily from mares on the periphery of the farm, 15 (60%) reported these fields were adjacent to non-equine premises, subdivisions or railroads.


Based on information from the 92 farms, the overall EFL rate was lower in 2002, with fewer farms having EFL losses in 2002.  Multiple control measures were undertaken to limit exposure of broodmares to ETC on the majority of farms.  This indicates that future approaches to limit broodmare exposure to the ETC will be multi-faceted.

Thanks are due to the Kentucky Thoroughbred Farm Managers Club and the Kentucky Thoroughbred Association for their support of this project, and to the farm managers and their staff who generously participated.

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