الفهرس 
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Abstract
This thesis concerned with the study of seasonality in mares in Egypt by conducting both ultrasound examination in 376 mares all year months and by assaying progesterone hormone (in absence of large ovarian follicles to confirm ovulation and corpus luteum formation). In addition, four cycling mares undergo daily blood sampling and ultrasound examination each other day for studying ovarian dynamics during the estrous cycle. Progesterone hormone was also assayed during the estrous cycle in addition to estrogen, leptin and Insulin- like growth factor –I to study their role in reproduction during the estrous cycle. This study found that progesterone hormone >1ng /ml was recorded during all year months leading to the conclusion that there was no seasonality in mares in Egypt, and this absence in seasonality in mare reproduction is also confirmed by monitoring large ovarian follicles>30mm in diameter during autumn, winter, spring and summer. Moreover, corpora lutea and different stages of pregnancy were also monitored during autumn and winter season. The studying of estrous cycle and ovarian dynamics is another confirmation to absence of seasonality and anestrum during summer. Regarding the ovarian dynamics, follicles of the next ovulation start to grow from days 5 and 6 of the estrous cycle and deviation to dominance start midway during the interovulatory interval on day 11. Largest ovarian follicle starts to increase in diameter from day 10 and continue in growth un till day of ovulation. Largest ovulatory follicle ovulate at a diameter >35mm. Interovulatory interval was 18 to 21 days (average20.25) and estrous phase was 5-7 days. Progesterone hormone was low from 3 to 4 days before ovulation and 2 days after ovulation un till the development of the new corpus luteum. Corpus luteum was recorded 2 days after ovulation and increased in diameter to reach a mature diameter of 40 mm the regress again before next ovulation. Estrogen hormone increases with the increase in diameter of the first large follicle and decline shortly before ovulation. A high estrogenic animal is also recorded compared to the other animals studied. Leptin hormone increase on days 5, 10, 14 and 18 of the estrous cycle and declined before ovulation. Insulin- like growth factor –I concentrations were low during early luteal phase and a small peak was noticed on day 2 then high peaks were observed on days 8, 11, 15 and 18 with the growth of the medium follicles and their deviation to dominance then maturation.