Objective—To determine whether administration of
killed West Nile virus vaccine was associated with
pregnancy loss among broodmares.
Design—Retrospective cohort study.
Procedure—Records of pregnant mares with known
vaccination history from 4 farms were reviewed.
Information obtained from 595 mares included mare's
identification; farm; age; breed; reproductive status;
last breeding date; date last known pregnant; vaccination
date; age of conceptus at vaccination; vaccination
during the early embryonic, early fetal, and late fetal
periods; and whether an early embryonic death (EED),
early fetal loss (EFL), or late fetal loss (LFL) occurred.
The relationships between the dichotomous outcomes
of loss (eg, EED, EFL, LFL) and independent categoric
variables (eg, vaccination during the early embryonic,
early fetal, or late fetal periods) were examined.
Results—Vaccination of pregnant mares during any
period of gestation was not associated with increased
incidence of pregnancy loss.
Conclusions and Clinical Relevance—Many mares
are already pregnant at the onset of mosquito season,
when mares are more likely to be vaccinated than at
other times. Our findings provide evidence that vaccine
administration will not compromise pregnancy in
horses. (J Am Vet Med Assoc 2004;225:1894–1897)
Objective—To determine features of an early fetal
loss (EFL) syndrome and evaluate potential risk factors
for EFL in Thoroughbred broodmares on 4 farms
in central Kentucky.
Animals—288 pregnant broodmares.
Procedure—Year-2001 breeding records for 288
Thoroughbred broodmares were examined. Early
fetal loss was defined as loss of a fetus that was
viable at ≥ 40 days of gestation but was subsequently
lost by 5 months of gestation.
Results—Overall 2001 EFL rate was 25% (73/288),
median gestational age at time of fetal loss was 77
days, and median date of loss was May 7. Mares on
1 farm had significantly fewer fetal losses (5%) than
mares on the other 3 farms (26 to 35%). Fetal losses
were higher for maiden (42%) and barren (42%)
mares than for foaling mares (18%). Fetal losses
were greater in young than in older mares. Effects of
broodmare farm, mare age, and reproductive status
were all significant. Fetal losses were not associated
with sire used for mating or stud farm.
Conclusions and Clinical Relevance—Greatest risk
for EFL occurred during the period from late April to
May (ie, in mares bred during February through
March). Higher incidence of EFL in maiden and barren
mares and lower incidence of EFL on 1 farm suggest
management or environmental influences may have
affected outcome. Risk factors that should be investigated
include environmental differences among
farms and differences in management procedures
used for lactating versus nonlactating mares. (J Am
Vet Med Assoc 2002;220:1828–1830)