Duration of gestation in pregnant dogs carrying cloned fetuses

The aim of this study was to investigate gestation duration and the physiologic characteristics of pregnant dogs bearing cloned fetuses, especially in the prepartum period. A retrospective study was performed to compare gestation duration in females pregnant with cloned (somatic cell nuclear transfer) fetuses (cloned group) with those bearing noncloned fetuses (control group), and effects of litter size, birth weight, and breed of somatic cell donors on gestation duration in the cloned group were evaluated. Clinical delivery onset signs associated with serum progesterone concentration and rectal temperature were also compared in both groups. The gestation duration calculated from day of ovulation was significantly longer in the cloned (62.8 ± 0.3 days) versus the control group (60.9 ± 0.5 days; P < 0.001). There was a negative correlation between litter size and gestation duration including both groups (r = -0.59; P < 0.01), but there were no differences between birth weights or breed of cell donors and gestation duration in the cloned group. Even though the basal rectal temperature in the prepartum period was not different between control and cloned groups (36.9 ± 0.1 °C and 37.2 ± 0.1 °C, respectively), serum progesterone concentration on delivery day was significantly higher in the cloned group (2.2 ± 0.4 ng/ml) compared with the control group (0.5 ± 0.1 ng/ml; P < 0.05). The longer gestation duration of pregnant dogs bearing cloned fetuses might be because of the smaller litter size in this group. Also, the weaker drop in serum progesterone levels in the prepartum period in cloned dog pregnancies indicates that the parturition signaling process might be altered resulting in longer gestation periods.