The pregnancy rate in indigenous ewes inseminated with frozen-thawed Suffolk semen following natural and synchronized estrus was determined. The serum Progesterone and Estrogen concentration and vaginal electrical resistance (VER) of ewes at the time of Artificial Insemination (AI) were observed as successful pregnancy determinants. 21 healthy ewes were selected for this experiment during January-April, 2017. 10 ewes were inseminated in natural estrus. Whereas, 11 ewes were inseminated after estrus synchronization using intravaginal sponges containing 60 mg medroxyprogesterone acetate. Trans-cervical Al (TCAI) was performed in all ewes within 12-16 hours of observed heat. Prostaglandin E1 analogue impregnated vaginal sponge was used for cervical relaxation 6-8 hours before insemination. Pregnancy was diagnosed through trans-abdominal ultrasonography after 40 days of AI. The pregnancy rate of ewes in synchronized estrus was higher (54.5%) than in natural estrus (30%). Higher serum Progesterone level (0.90 ± 0.02 ng/mL) and significantly (p < 0.001) lower VER (257.78 ± 10.11 ohm) were observed at the time of AI in ewes becoming pregnant. Results suggest that higher Progesterone concentration and lower VER could be considered as pregnancy indicators. Oestrous synchronization could be implemented to increase the pregnancy rate in ewes.

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS
CONFLICTS OF INTEREST
ACKNOWLEDGEMENTS
AUTHOR CONTRIBUTIONS
AUTHOR’S POSITION AND ORCID NO
REFERENCES

• Mahbubur Rahman(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Nazmun Naher(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Mofijul Isam(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Moinul Hasan(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Farhana Naznin(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Mohammad Musharraf Uddin Bhuiyan(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Farida Yeasmin Bari(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh)
• Nasrin Sultana Juyena(Department of Surgery and Obstetrics, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh) Corresponding author