A COMPARATIVE STUDY OF OVINE PLACENTAL LACTOGEN AND PROLACTIN SECRETION PATTERNS IN GENETICALLY DISSlM I LAR FETAL CO-TWINS 1

Simultaneous fetal and maternal ovine placental lactogen (oPL) and prolactin (oPRL) measure- ments were determined from blood samples collected from six mixed breed (MB; gestation = 141.5 -* .7 d) pregnancies and single Rambouillet (n = 2; Ra gestation = 148 and 149 d) and Finnish Landrace (n = 2; Finn gestation = 141 and 143 d) pregnancies for the purpose of examining a possible relationship between fetal-maternal oPL and oPRL levels in the prepartal period. The MB pregnancies were produced by embryo transfer and consisted of genetically different fetuses co-existing in a common uterine environment. Despite the apparent prematurity of Ra co-twins in MB pregnancies, similar oPL and oPRL patterns during the final 14 d of gestation were observed for both Ra and Finn co-twins. Fetal oPL levels decreased at parturition (range 23 to 90 ng/ml) to approximately 6096 of values recorded 8 d prepartum (range 100 to 150 ng/ml) in both fetal siblings. Increases in fetal oPRL concentrations, first observed at approximately 4 d prepartum in all fetuses, reached peak concentrations (40 to 60 ng/ml) at term. Results of this study suggest a similarity in regulation of fetal oPL and oPRL secretion, despite genetic differences for gestation period, in fetuses in the M.B. pregnancy.