Objective—To estimate risk of exposure and age at
first exposure to Sarcocystis neurona and Neospora
hughesi and time to maternal antibody decay in foals.
Animals—484 Thoroughbred and Warmblood foals
from 4 farms in California.
Procedure—Serum was collected before and after
colostrum ingestion and at 3-month intervals thereafter.
Samples were tested by use of the indirect fluorescent
antibody test; cutoff titers were ≥ 40 and
≥ 160 for S neurona and N hughesi, respectively.
Results—Risk of exposure to S neurona and N hughesi
during the study were 8.2% and 3.1%, respectively.
Annual rate of exposure was 3.1% for S neurona and
1.7% for N hughesi. There was a significant
difference in the risk of exposure to S neurona among
farms but not in the risk of exposure to N hughesi.
Median age at first exposure was 1.2 years for S neurona and
0.8 years for N hughesi. Highest prevalence
of antibodies against S neurona and N hughesi was
6% and 2.1%, respectively, at a mean age of 1.7 and
1.4 years, respectively. Median time to maternal antibody
decay was 96 days for S neurona and 91 days for
N hughesi. There were no clinical cases of equine protozoal
Conclusions and Clinical Relevance—Exposure to
S neurona and N hughesi was low in foals between birth
and 2.5 years of age. Maternally acquired antibodies
may cause false-positive results for 3 or 4 months after
birth, and EPM was a rare clinical disease in horses ≤ 2.5
years of age. (Am J Vet Res 2004;65:1047–1052)