Urinary Estrogen Excretion Rates During Pregnancy in the Bovine

Urine was collected from 48 cows from 101 to 285 days of pregnancy, to define urinary excretion rates of estrone, 17 flestradiol, 17 a-estradiol, and an incompletely identified triol, hereafter referred to as estriol. Enzyme hydrolysis was used as the first extraetion step to minimize destruction of 17 a-estradiol. The estrogens were separated and purified by paper partition chromatography and measured fluorimetrically. Breed, age, and live weight of the eow were not significantly related to excretion rate when the latter was adjusted to a 5(~0-kg basis (~g/hr-live weight 500 kg). Average total estrogen excretion _+_ one standard error per hour per 500 kg during pregnancy was as follows: 101 to 123 days--300 96 /~g; 165 to 175 days--581 154 /x~o", 200 to 212 davs--489. -136 ~g: 226 to 237 days--691 104 /~g; 250 t. 254 days--l,809 580 ~g: and 271 to 285 days--3,402 412 ug. The latter two means were significantly higher than means of each of' the other periods. Estriol excretion was highest during 250 to 254 days (P < 0.01, except for 226 to 237 days). Changes in 17 fl-estradiol were not significant, but estrone increased significantly (P < 0.01) by 271 to 285 days and 17 a-estradiol increased significantly (P < 0.01) by 250 to 254 days. Excretion rate of estrone tended to be higher or equal to 17 a-estradiol through 237 days, but 17 a-estradiol increased tenfold thereafter, compared with a fourfold increase for estrone.