Non-Instrumented Immunoassay Field Tests for Pregnancy Detection in Free-Roaming Feral Horses

We evaluated 2 rapid non-instrumented field tests for pregnancy on feral horses (Equus caballus) because previous techniques required sophisticated and expensive instrumentation that limited their usefulness to field researchers. The measurement of urinary estrone conjugates ($\text{E}_{1}\text{C}$) by an enzyme immunoassay and based on observable color changes was 100% accurate when compared with instrumented spectrophotometrically measured tests for$\text{E}_{1}\text{C}$. A non-instrumented "dipstick" enzyme immunoassay for equine chorionic gonadotropin-like (eCG) molecules was 83% accurate in diagnosing mare pregnancies when compared with the results of the instrumented test for$\text{E}_{1}\text{C}$. The decrease in accuracy using the non-instrumented eCG test resulted from a time period of 40-140 days when eCG was measurable, whereas$\text{E}_{1}\text{C}$elevations were measurable after day 35 of a mare's pregnancy. Our results indicate that it is possible to detect pregnancy in free-roaming horses under field conditions and without instrumented assays; such field tests provide opportunities to study fecundity and fetal loss in a variety of free-roaming animals.