Monitoring luteal function in the lion‐tailed macaque (Macaca silenus) through urinary progesterone metabolite measurements

A direct radioimmunoassay for measuring urinary 20‐hydroxyprogesterone cross‐reactivity to monitor and assess luteal function and detect pregnancy in the lion‐tailed macaque (Macaca silenus) is described. Urine samples were collected daily during ten nonconceptive and five conceptive ovarian cycles of five dult female lion‐tailed macaques. Urine was analyzed for concentrations of 20α‐hydroxypro‐gesterone cross‐reactivity, estrone conjugates, and creatinine. The strength of the luteal phase in normal nonconceptive cycles (n = 8) is characterized by a maximum sevenfold increase (day 9) in mean 20α‐hydroxyprogesterone cross‐reactivity over follicular phase levels; the duration, by a 13‐day sustained elevation of mean 20α‐hydroxyprogesterone cross‐reactivity levels. Pregnancy is detectable from 20α‐hydroxyprogesterone cross‐reactivity values approximately 20 days after the periovulatory estrone conjugate peak (n = 4). Apparent anovulation (n = 1), extended follicular phase (n = 1), and early abortion (n = 1) also are detectable using 20α‐hydroxyprogesterone cross‐reactivity measurements.