الفهرس 
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Abstract
The present study included two experiments. The aims of the first experiment, was to evaluate the fertility response, in terms of conception rates, to modified PRID-synch, eCG-synch and Insulin-synch in comparison with Basic-ovsynch in cyclic and acyclic cows. Also, the follicular dynamics and hormonal profiles of progesterone, Estradiol and Insulin that occurs in concomitant with application of PRID-synch, eCG- synch and Insulin-synch in comparison with Basic-ovsynch were followed up in cyclic and acyclic cows. The aim of the second experiment was to test whether the insertion of either progesterone-releasing intra-vaginal device (PRID) or controlled internal drug releases (CIDR) between Day 1 and Day 9 (day 0 is day of insemination) post- insemination improve pregnancy per AI (P/AI) in high lactating dairy cows or not.
The results of the first experiment it could be concluded that: The PRID-synch protocol (PRID was inserted between days 0 and 7 of Basic-ovsynch) achieved the highest fertility response in cyclic (CR, 50% Vs 30% in control) and acyclic cows (CR, 30% Vs 20% in control) cows. The Insulin-synch (Insulin was injected S/C on Days 7, 8 and 9 of Basic-ovsynch) achieved the same fertility response as PRID-synch while eCG-synch (1000 IU eCG was injected on Day 7 of Basic-ovsynch) achieved relatively lower fertility response (CR, 40% Vs 30% in control) in cyclic cows.
from the results of the second experiment, it could be concluded that exogenous administration of P4 via insertion of P4 releasing intravaginal devices (IVPD) that induces earlier increase (≈ day 3 postinsemination) in the circulating P4 concentration regardless the level of the increase is beneficial in improving conception rate in high lactating cows.