Evaluation of an oestrone sulphate dipstick immunoassay for pregnancy testing mares

Serum samples from 213 mares were received for routine pregnancy testing and analysed by a conventional oestrone sulphate (OS) enzymeimmunoassay (EIA) and a new OS dipstick immunoassay. OS concentrations, measured by EIA, in 122 of the samples were 20 ng/ml. Of these, 89 also returned a ‘pregnant’ diagnosis by the dipstick assay, but 2 returned a ‘not pregnant’ diagnosis. Both these mares were found to be pregnant on follow up, indicating that the dipstick test had returned a false negative diagnosis in each instance. These results show that there is 100% agreement between the conventional OS EIA and the new dipstick assay in diagnosing ‘non pregnancy’. However, the dipstick assay may return a small proportion (2.2%) of false negative diagnoses relative to the EIA. Overall, the new dipstick immunoassay offers a practical alternative to the OS EIA for diagnosing pregnancy status in mares.