Monitoring of corpus luteum function by measuring progestagens in faeces of non-pregnant mares (Equus caballus) and Przewalski mares (Equus przewalski).

Faecal samples were collected daily from 12 Warmblood mares and five Przewalski mares for 4-7 weeks in spring. Blood samples from nine Warmblood mares were taken one to two times a week. In faecal samples the concentration of progestagens was determined using a radioimmunoassay (RIA) and an enzyme-immunoassay (EIA) for 20alpha-dihydroprogesterone (20alpha-G) and an EIA for 20beta-dihydroprogesterone (20beta-G). In seven Warmblood mares the concentrations of progesterone (P4) in plasma (RIA) and progestagens in faeces revealed a cyclic pattern. When comparisons were made for faecal steroids in samples corresponding to lower (less than 1 ng ml-1) and higher (more than 2 ng ml-1) plasma P4 concentrations, a significant difference (P<0.05) for each progestagen assay was noted (20alpha-G RIA: 58 +/- 23 ng g-1, 161 +/- 67 ng g-1; 20alpha-G EIA: 90 +/- 64 ng g-1, 156 +/- 86 ng g-1; 20beta-G EIA: 145 +/- 98 ng g-1, 367 +/- 173 ng g-1 faeces respectively). The coefficients of correlation between plasma P4 and the faecal 20alpha-G RIA, 20alpha-G EIA and 20beta-G EIA were 0.69, 0.47 and 0.59 respectively (P<0.01). Four Przewalski mares showed concentrations of faecal progestagens, which were indicative of an oestrous cycle. The remaining mare showed a low concentration of faecal progestagens. The values of 20alpha-G in faeces were comparable, whereas concentrations of 20beta-G were only half of those in Warmblood mares. Supporting evidence for the methodology used was obtained using high-performance liquid chromatography (HPLC) followed by RIA and EIA for extracts of selected samples. It was concluded that different assays for the determination of progestagens in faecal samples of equine species are suitable for non-invasive monitoring of the oestrous cycle.