Relationship between Serum Concentrations of Placental Steroids in Dams and the Birth Weight and Viability of Newborns in Japanese Black Cattle

Abstract

To monitor the feto-placental function, blood samples were collected by jugular venipuncture from 54 dams at 257 (4 weeks before due date: -4W) and 271 (2 weeks before due date: -2W) days of gestation. Serum progesterone levels (P) were measured by enzymeimmunoassay. Free estrone(E₁), estradiol-17β (E₂) and estrone sulfate(E₁S) in the serum were measured by radioimmunoassay. After delivery, 54 dams were divided into two groups: a group of 41 dams with a newborn calf over 20 kg body weight (normal birth weight group; NBW), another group of 13 dams with a calf of 20 kg or less (low birth weight group; LBW). From -4W to -2W, slight decrease in P, significant increases in E_l and E₂ were observed, but no significant differences were present in those steroids between LBW and NBW. E₁S was significantly lower in LBW than in NBW (P<0.01) and correlated positively with the birth weight of calves (r=0.50, P<0.01) at -4W and -2W, respectively. In the 13 LBW calves, eight showed neonatal weakness and two of them died, while the other 5 calves did not show the weakness. Eight LBW calves with neonatal weakness had a relatively lower maternal E₁S level than the other 5 viable calves at -4W, and it remained at the same level at-2W. In contrast, the 5 vital calves with LBW showed a significant increase of maternal E₁S from -4W to -2W. These results suggest that maternal serum E₁S level provides useful and practical information for monitoring the feto-placental function and for predicting the maturity and viability of newborn calves.