Changes in pelvic conformation and peripheral estrone concentrations in pre- and post-partum beef cows

Abstract

An experiment was conducted to investigate the temporal relationship of peripheral estrone (E 1) concentration to changes in the size of the pelvic opening preceding and immediately following parturition. Twenty-six multiparous beef cows were observed from approximately 50 d prepartum to 7 d postpartum. Blood samples were collected at 7 d intervals preceding calving and at 1, 3 and 7 d following for E 1 quantitation. Estimates of pelvic opening area were made at the time of blood sampling. Peripheral E 1 concentrations were elevated beginning at approximately 25 d prepartum. Dams bearing male fetuses had greater (P<0.01) concentrations E 1 than did dams with female fetuses. Calf birth weight was correlated (r = 0.44, P<0.01) with E 1 levels from 10 d prepartum through parturition. Postpartum pelvic area was greater for cows giving birth to male calves, with no significant differences for calf birth weights by sex. Correlations were observed between E 1 concentration, and pelvic area measured from 50 d prepartum to 7 d postpartum (r = 0.26, P<0.01), 10 d prepartum to calving (r = 0.42, P<0.01), and from calving to 7 d postpartum (r = 0.33, P<0.01). Percentage increase in E 1 concentration from 50 d prepartum to calving was significantly correlated (r = 0.75, P<0.01) to percentage pelvic area increase over the same period. A correlation also exists between maternal E 1 concentrations and fetal sex and pelvic area. In summary, the increased estrogen concentrations in cows with male calves may facilitate pelvic spread, resulting in a larger pelvic opening.