FOETAL AND MATERNAL HORMONAL CHANGES PRECEDING NORMAL BOVINE PARTURITION

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Abstract
Successful chronic cannulation of the fetal posterior vena caba and maternal utero-ovarian and jugular veins in 5 Jersey cows between days 240-260 of gestation enabled changes in plasma hormone levels preceding calving to be monitored. All cows delivered live calves within the expected range of gestation for the breed. Corticosteroids were assayed by competitive protein-binding, and prostaglandin [PG] F, progesterone, estrone and estradiol-17.beta. by radioimmunoassay. Fetal corticosteroids rose slowly from 5.0 .+-. 0.7 ng/ml at 20 days to 9.3 .+-. 3.0 ng/ml at 10 days before term, then progressively increased to a mean of 74 ng/ml at calving. Maternal levels remained relatively constant at 5-15 ng/ml, though higher concentrations occurred following surgery. Fetal estrone and estradiol-17.beta. concentrations were both less than 50 pg/ml and showed little change toward term. Maternal utero-ovarian estrogens increased slowly from 20 to 10 days pre-partum and then rose more rapidly reaching peak levels (2.9 .+-. 0.6 ng/ml for estrone and 1.4 .+-. 0.3 ng/ml for estradiol-17.beta.) 1-4 days before delivery. Maternal progesterone concentrations fell towards term, with a rapid decrease over the last 36-48 h. PGF levels showed little change until 36-48 h before calving when they gradually increased until the last 24 h, where there was a dramatic rise, reaching peak levels (5.7 .+-. 0.6 ng/ml) during labor.

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