Veterinaria México Publicación Digital de la Facultad de Medicina Veterinaria y Zootecnia OA / 17 1 Vol. 10  2023 Original Research https://veterinariamexico.fmvz.unam.mx/ Submitted: 2022-03-14 Accepted: 2022-10-27 Published: 2023-01-30 Additional information and declarations can be found on page 13 Copyright 2023 Essam A. Almadaly et al. open access Distributed under Creative Commons CC-BY 4.0 Abstract This study investigates the effect of estrus synchronization on the reproductive performance of Ossimi ewes during the early summer season to prove that they are cyclic throughout the year in subtropical climates. In June, 280 ewes were assigned to seven (n = 40) groups and received one of the following: 1) short-term progesterone (ST) P4 treated ewes received 20 mg P4 day after day for 6 days and 500 international unit (IU) equine chorionic gonadotropin (eCG) on day 6; 2) long-term P4 (LT) P4 treated ewes received 20 mg P4 day after day for 12 days and 500 IU eCG on day 12; 3) double prostaglandin (PG) F 2α 7days apart and 500 IU eCG on day 7 (PGF 2α -7d); 4) double PGF 2α 14 days apart and 500 IU eCG on day 14 (PGF 2α -14d); 5) traditional ovulation syn- chronization (T-Ovsynch; gonadotropin-releasing hormone (GnRH)-0 day; PGF 2α -5 day and GnRH-7 day); 6) non-traditional ovulation synchronization (NT-Ovsynch; GnRH-0 day; PGF 2α -7 day and GnRH-9 day); 7) control ewes received no treatment. There were significant differences among groups for estrus rate, the onset of estrus, pregnancy, and lambing rates as well as pro- lificacy and gestation period. The highest (90 %) estrus rate was recorded in (LT) P4, PGF 2α -14d, and NT-Ovsynch protocols while the lambing rate was the maximum (100 %) in PGF 2α -14d. Although all treatments had a positive effect on ewe fertility; long-term protocols particularly PGF 2α -14d; are rec- ommended to improve Ossimi ewe fertility during the early summer season. Keywords: Estrus synchronization; Ovsynch protocol; Ossimi ewes; PGF 2α ; Progesterone; Prolificacy. Comparison of estrus response and subsequent fertility following estrus synchronization with six protocols in Ossimi ewes during the early summer season Essam A. Almadaly 1* 0000-0003-3598-8090 Ferial Sahwan 2 0000-0001-8176-4763 El-Domany 3 Ahmed Radwan 1 Mustafa Shukry 4 0000-0003-2722-2466 Foad Farrag 5 0000-0002-4048-6717 1 Kafrelsheikh University, Faculty of Veterinary Medicine, Department of Theriogenology, El-Geish Street, Kafrelsheikh 33516, Egypt. 2 Alexandria University, Faculty of Veterinary Medicine, Animal Breeding and Production, Animal Husbandry and Wealth Development Department, Egypt. 3 Mansoura University, Faculty of Veterinary Medicine, Department of Theriogenology, Mansoura, Egypt. 4 Kafrelsheikh University, Faculty of Veterinary Medicine, Department of Physiology, El-Geish Street, Kafrelsheikh 33516, Egypt. 5 Kafrelsheikh University, Faculty of Veterinary Medicine, Department of Anatomy and Embryology, El-Geish Street, Kafrelsheikh 33516, Egypt. *Corresponding author: Email address: dr_essam_2005@yahoo.com Cite this as: Almadaly EA, Sahwan F, Wael B. E, Radwan R, Shukry M, Farrag F. Comparison of estrus response and subsequent fertility following estrus synchronization with six protocols in Ossimi ewes during the early summer season. Veterinaria México OA. 2023;10. doi: 10.22201/fmvz.24486760e.2023.1058. DOI: http://dx.doi.org/10.22201/fmvz.24486760e.2023.1058