Abstract
Plasma estradiol, estrone, progesterone, total corticoids and LH levels were measured in samples collected at 4-day intervals from 35 postpartum and cyclic lactating cows. Estrogens were extracted, purified on Sephadex LH-20 columns and quantitated by a radioimmunoassayusing ovine anti-estradiol and dextran coated charcoal separation. Progesterone and total corticoids were measured by a competitive protein binding assay. LH levels were determined by a double antibody radioimmunoassay procedure. Plasma estradiol concentrations were elevated at parturition (67.9 ± 24.4 pg/ml) as compared to 4 days later (10.3 ± 4.3 pg/ml plasma). Plasma corticoid levels also decreased following parturition. Plasma progesterone and LH values remained at a low level (0.0 to 0.3 ng/ml plasma and 0.5 to 3.0 ng LH-B7/ml plasma, respectively) from parturition until first estrus. Estradiol concentration began to rise 2 to 3 days prior to estrus, but declined rapidly after estrus. Changes in plasma estrone levels paralleledthose of estradiol. Preovulatory LH peaks ranged from 7 – 55 ng LH-B7/ml of plasma with levels of 0.5 – 3.0 ng during the remainder of the cycle. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.