FOETAL AND MATERNAL HORMONAL CHANGES PRECEDING NORMAL BOVINE PARTURITION

Abstract

ABSTRACT Successful chronic cannulation of the foetal posterior vena cava and maternal utero-ovarian and jugular veins in five Jersey cows between days 240 and 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 F, progesterone, oestrone and oestradiol-17β by radioimmunoassay. Foetal 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 to 15 ng/ml, though higher concentrations occurred following surgery. Foetal oestrone and oestradiol-17β concentrations were both less than 50 pg/ml and showed little change toward term. The maternal uteroovarian oestrogens increased slowly from 20 to 10 days pre-partum and then rose more rapidly reaching peak levels (2.9 ± 0.6 ng/ml for oestrone and 1.4 ± 0.3 ng/ml for oestradiol-17β) 1 to 4 days before delivery. Maternal progesterone concentrations fell towards term, with a rapid decrease over the last 36–48 h. Prostaglandin F levels showed little change until 36–48 h before calving when they gradually increased until the last 24 h where was a dramatic rise, reaching peak levels (5.7 ± 0.6 ng/ml) during labour.