42 PREPARTUM HORMONAL CHANGES IN RECIPIENT COWS FOR SOMATIC CELL CLONED FETUSES

Abstract

Placental estrogens are associated with fetal growth and development, and play important roles in the initiation of the parturition process. In the delivery of somatic cell-cloned (SC) calves, recipient cows show a weak and unclear symptom of parturition, although large offspring syndrome (LOS) frequently occurs. The mortality of calves by dystocia decreases the efficiency of SC cattle production. In this study, we examined peripheral estrone (E1), estradiol-17² (E2), estrone sulfate (E1S), and progesterone (P4) levels during preparturition in recipients of SC and in vivo calves. Recipients were administered 20 mg dexamethasone (DEX) at Days 276-288 of pregnancy, followed by 0.75-1 mg cloprostenol (PG) and 20 mg estriol 24 h later. Calves (Japanese black cattle) were delivered 2 or 3 days after the DEX administration. SC calves were delivered by cesarean section (C-sec) when LOS was suspected by rectal palpation. Blood samples of recipients [vaginal delivery of SC (Vag): n = 13; C-sec of SC: n = 8; vaginal delivery of in vivo calves (Control): n = 4] were taken at Days 257 and 271 of pregnancy, and just before DEX (-2P), PG (-1P), and parturition (0P). Blood samples of calves were taken just after delivery to analyze cortisol level. The statistical significance was analyzed by the Steel-Dwass test. Birth weight of calves was the heaviest (P < 0.05) in C-sec (62 ± 3 kg; n = 12); Vag calves (43 ± 2 kg; n = 19) were also heavier (P < 0.05) than Control calves (29 ± 2 kg; n = 9). E1 levels in Control calves remained low (<629 ± 111 pg mL^-1) until Day 271 and then increased progressively (>2156 ± 599 pg mL^-1). E1 levels tended to be lower in Vag (<1968 ± 299 pg mL^-1) and C-sec (<1268 ± 385 pg mL^-1) calves at -2P, -1P, and 0P; E1 levels in C-sec calves were significantly lower (P < 0.05) than in Control calves at -2P (512 ± 85 pg/mL^-1) and -1P (725 ± 91 pg mL^-1). The E2 level in Control calves increased and reached a plateau at -2P. Vag and C-sec calves showed lower E2 levels, except that the Vag level at 0P was similar to that in Control calves. The E2 level of C-sec calves (61.8 ± 25.3 pg mL^-1) at 0P was significantly lower (P < 0.05) than that of Control calves (247.5 ± 102.8 pg mL^-1). E1S levels in Vag and C-sec calves increased progressively from -2P to 0P, whereas the E1S level in Control calves increased at 0P. The E1S level in Vag calves (41.1 ± 4.1 ng mL^-1) was significantly higher (P < 0.05) than in Control calves (19.4 ± 5.1 ng mL^-1) at -1P. P4 levels decreased from -2P in Vag and Control calves, and from -1P in C-sec calves. The cortisol level in C-sec calves (60.1 ± 19.1 ng mL^-1) tended to be low compared with that in Vag (104.4 ± 23.1 ng mL^-1) and Control (93.4 ± 15.0 ng mL^-1) calves. This study revealed fetoplacental dysfunction of estrogen synthesis in the SC fetus during preparturition. Elevated E1S levels in recipients of the SC fetus, which correlated with high birth weight and agreed with previous reports for normal or plural pregnancy, might cause the reduction of E1 level. The comparable level of cortisol in Vag and Control calves indicated that SC calves had normal adrenal cortex function. Further analysis on placental estrogen synthesis and cortisol secretion in the SC fetus is necessary to clarify the cause of the prolonged gestation.