عنوان مقاله [English]
Introduction: Reproduction is directly affected by various management related factors. Manipulation of these factors can cause changes in reproductive performance. The reproductive performance is considered as the most important factor in determining the profitability of ruminant breeding. Estrous synchronization and supper ovulation are considered as the two valuable management tools used to increase the efficiency of reproduction in small ruminants and seasonal breeder animals, thanks to the use of hormonal therapies The control and manipulation of the sheep reproduction has been the objective of scientists around the world for many years. Identifying the appropriate foreign and indigenous breeds to improve reproductive performance is an essential requirement for self-sufficiency of sheep products. Intensive lamb production systems involve the obtention of more than one lambing per ewe per year. Accelerated lambing systems require the implementation of two, three or even five breeding periods at different times of the year. The purpose of this study was to investigate the effects of using CIDR and PMSG as an appropriate method of concomitant with artificial insemination of imported ewes and comparing them with native Iranian ewes on reproductive performance.
Materials and methods: The experiment was conducted at the Research Unit Farm of the Light Livestock Breeding Center of the Water and Soil Conservation Company, located in the southern Khorasan province, Iran. 180 ewes with average weight of 50 ± 1.5 kg were divided into 6 groups of 30 rats based on internal and external breeds including: 1- Romanov group 2- Sharouleh group 3- Suffolk 4- Baluchi 5- Mogani group 6- Afshari were selected. Estral synchronization was performed in spring with CIDR. Ewes after CIDR (14 day) extraction and PMSG injection as soon as the signs of estrus were observed, the ewes were isolated from the others and artificially inseminated with fresh sperm using the transcortical method. Ultrasonography examination was performed by an ultrasound device (6 MHz linear probe, ECM model, France). The nutrition program with software (SRNS) version was adjusted based on the pregnancy diet. Investigation of the number of graafian follicles (follicles larger than 4 mm), was examined simultaneously with CIDR removal and estrus observation. Then, in each experiment parameters such as the time of estrus initiation (hour), rate of return to estrus, parturition rate, rate of multiple births, number of lambs and rate of lambing were evaluated.
Results and discussion: There were no difference between the experimental groups in terms of estrus symptoms. Results showed that Ovarian ultrasound at day 10 postoperatively showed that the number of lutein in foreign races was higher than other races and significant statistical differences were observed (p<0.05). The results of the present study showed that the mean daily body weight change of ewes was affected by experimental groups (p<0.05). Ovulation in most ewes, depending on the breed, occurs at a fixed time in relation to the onset of estrus. The breed of ewe could be one of the factors influencing the time of ovulation. Results Ovulation rate, Pregnancy rate, stillbirth rate, was significant difference in fertility rate and twinning rates between the groups (P <0.05). The highest ovulation rate (100%), pregnancy rate (100%), The fertility rate (160%) and Twinning rates (66%) belonged to the Romanov group and statistical differences were observed (p<0.05). Variability between results could be attributed to different protocols, management systems, nutritional status or physiological status resulting from diverse experimental conditions. Furthermore, these variable results may indicate that breed, timing of treatment or doses used in these treatments produce critical effects on fertility rate and embryo survival.
Conclusion In general, the use of some new technologies such as estrous cycle control and the use of hormones was effective in this study and increased the average production of lambs per ewe mixed in the herd. Significant differences between Romanov ewes in pregnancy rate, lambing rate and twinning with other breeds indicate the high genetic capacity of this breed of sheep in the success of reproductive performance. Due to low productivity of Iranian breeds compared to foreign breeds, it can be suggested that foreign sheep be used to improve breeding efficiency of Iranian sheep for breeding.