Pregnancy determination in uncaptured feral horses based on steroid metabolites in urine-soaked snow and free steroids in feces

Abstract

Urine-soaked snow from 13 uncaptured feral mares was collected and measured without extraction for estrone conjugates (E1C) and nonspecific immunoreactive pregnanediol-3-glucuronide (iPdG) by enzyme immunoassays. The hormone values were indexed to creatinine (Cr). Mares that produced foals had urinary E1C values of 7.30 ± 1.39 (SE) μg/mg Cr versus 0.096 ± 0.084 μg/mg Cr for mares that did not produce foals. The difference was significant (P < 0.001). Nonspecific iPdG concentrations for mares producing foals was 167 ± 80.33 ng/mg Cr versus 7.04 ± 1.69 ng/mg Cr for mares that did not produce foals. The difference was significant (P < 0.0025). Urine samples collected directly from the ground from 34 uncaptured feral mares were measured for E1C and nonspecific progesterone metabolites and compared with fecal total estrogen concentrations in matched fecal samples, measured by means of radioimmunoassay. Both E1C and iPdG concentrations differed significantly (P < 0.001) between mares producing foals and those that did not. Mean fecal total estrogen concentrations for mares producing foals was 3.18 ± 0.70 ng/g feces versus 0.552 ± 0.08 ng/g feces for those that did not produce foals. The difference was significant (P < 0.001). The correlation coefficient between urinary E1C and fecal total estrogens was 0.928. The results indicate that both urine-soaked snow and fecal samples can be used to reliably assess pregnancy in uncaptured free-roaming feral horses.