Abstract: [Objective] This study aimed to investigate the effects of crossbreeding of Australian White sheep as paternal parents and Hulun Buir sheep as maternal parents on reproductive performance and reproductive hormone secretion during gestation period of ewes. [Method] A total of 392 Hulun Buir ewes were selected and randomly assigned into an experimental group or a control group according to the ram breeds. For the ewes in the experimental group （n=139）, Australian White sheep （n=7） were served as the breeding ram, while for those in the control group （n=253） , Hulun Buir sheep （n=13） were served as the breeding ram. After delivery, the reproductive performance indicators such as conception rate, miscarriage rate and twinning rate of the ewes in the two groups, as well as the birth weights of the lambs produced by the ewes in the two groups were statistically compared. Eight ewes were selected from each group, and blood samples were collected at mid-gestation period （60 d gestation）, late-gestation period （90 d gestation） and 10 d before the expected date of lambing, respectively. The serum levels of follicle-stimulating hormone （FSH）, luteinizing hormone （LH）, progesterone （P₄） and estradiol （E₂） were measured with ELISA kits.[Result] The ewes in the experimental group had significantly （P<0.05） lower conception rate and actual delivery rate, significantly （P<0.05） higher miscarriage rate, and extremely significantly （P<0.01） higher twinning rate compared with those in the control group. No significant （P>0.05） difference in lamb survival rate between the experimental group and the control group was observed. There were no significant （P>0.05） differences in the lamb birth weight, single-lamb birth weight and twin-lamb birth weight between the experimental group and the control group. At each observed time points during gestation period, the serum levels of FSH, LH, P₄ and E₂ of the experimental group ewes had no significant （P>0.05） differences with those of the control group ewes. For the ewes in the control group, there were no significant （P>0.05） differences in the serum levels of LH, FSH and E₂ among the three observed time points during gestation period, while the serum level of P₄ at 10 d before the expected date of lambing was significantly （P<0.05） higher than that at the mid- and late-gestation period. For the ewes in the experimental group, the serum level of E₂ at the late-gestation period was significantly （P<0.05） higher than that at the mid-gestation period and 10 d before the expected date of lambing; the serum level of E₂ at the mid-gestation period was significantly （P<0.05） higher than that at 10 d before the expected date of lambing; the serum level of P₄ at the late-gestation period and 10 d before the expected date of lambing was significantly （P<0.05） higher than that at the mid-gestation period. [Conclusion] Crossbreeding of Australian White sheep as paternal parents and Hulun Buir sheep significantly elevated the twining rate and thus improved the reproductive efficiency of ewes, indicating that Australian White sheep as paternal parents had heterosis in improving the reproductive performance of Hulun Buir sheep.

Key words: Hulun Buir sheep, crossbreeding, Australian White sheep, reproductive efficiency, reproductive hormone