الفهرس 
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Abstract
This study was conducted at Stations of El-Karada and Sakha and International Livestock Management Training Center, Sakha, Kafrelshiekh, belonging to Animal Production Research Institute, Agricultural Research Center, Ministry of Agriculture in cooperation with Animal Production Department, Faculty of Agriculture, Mansoura University during the period from January 2017 to March 2018. This study aimed to compare the effect of using PMSG at a level of 2500 IU in term of one dose, two doses (1250 IU/dose) or 4 doses (625 IU/dose) on follicular dynamics, in term of follicular dynamics on the ovarian surface on the right and left sides, as well as progesterone in blood serum of cows, on different protocol days. Super-ovulatory response, embryo production and cryopreservation by vitrification were evaluated. Total of 21 Friesian cows (450-550 kg LBW, 3.5-5.5 y old and 1-3 parities) were used as embryo donors. All cows were i.m. injected with 3 ml PGF2α/cow for estrous synchronization. Cows in the 1st protocol (P1) were i.m. injected with one dose of PMSG (2500 IU/cow) on day 10 of estrous cycle (control), while those in the 2nd and 3rd protocols were i.m. injected with two doses of PMSG (1250 IU/dose/cow) at 12 h interval on day 10 of estrous cycle (P2) and with four doses of PMSG (625 IU/dose/cow) at 12 h interval on day 10 and 11 of estrous cycle (P3), respectively. After 48 hours of the last PMSG dose, all cows were i.m. injected with 2 ml PGF2α/cow. Both AI and GnRH (5 ml /animal) injection were done on day 14 in P1 and P2 and day 15 in P3. Number of total follicles, large follicles and CLs, and diameter of follicles for each cow in each protocol were determined, while progesterone profile was assay on different protocol days. Ovulation rate, recovery rate, yield, quality and stage of non-surgical embryos recovered 7 days post-AI were determined. The obtained results can be summarized as follows: * Follicular number: - Number of total and large follicles through different days of each protocol revealed nearly similar trend of increase up to day of AI, being the greatest in P3, followed by P2 and P3, respectively. - Thereafter, there was a marked reduction in follicular number on day of flushing, being sharper in P3 than in P1 and P2. The gradual increase in number of total and large follicles was recorded post-PMSG injection. - On day of flushing, the sharp reduction in number of total follicles in all protocols surely indicated ovulation of considerable number of ovarian follicles, being greatest for cows in P3, followed by P1 and the least in P2. Follicular diameter: - Following PMSG injection, diameter of total and large follicles of the 2nd follicular wave gradually increased up to day of AI under the effect of PMSG dose in all protocols, being the widest in cows of P3, followed by P2 and the narrowest in P1. - On day of flushing, there was other gradual increase in diameter of total follicles due to ovulation, whereas the recorded follicular diameter on day of flushing represent diameter of un-ovulated follicles following AI, these follicles were with narrower diameter in P3 than in P1 and P2. Serum progesterone profile on different protocol days: - On day of flushing, the observed maximal P4 level was in association with number of CLS induced by ovulation as affected by PMSG injection, being the highest in P3, moderate in P1 and the lowest in P2. - Overall mean of P4 concentration on day of estrus significantly (P<0.05) increased on day of PMSG injection and showed insignificant increase on day of PGF2α, then significantly (P<0.05) increased to the maximal levels on day of flushing. However, overall mean of P4 concentration was not affected significantly by protocol. Super-ovulatory response (SOR): - The SOR, in term of CLs formation on day of flushing, all cows (100%) in each protocol showed CLs on the right, left or both ovaries. Percentage of responded cows showing CLs on the right ovaries was higher than those showing CLs on the left ovaries in P1 (85.7 vs. 71.4%), being the opposite in P2 (71.4 vs. 85.7%) and similar in P3 (85.7 on each side). - Ovulation rate was significantly (P<0.05) higher in P1 than in P2 (75.68 vs. 55.0%), but did not differ significantly in P3 (63.04%) from that in P1 and P2. Conclusion: In conclusion, Super-ovulation of Friesian cows with PMSG (2500 IU/cow) on day 10 of the estrous cycle, in term of 4 doses (625 IU) at 12-h intervals, showed the best follicular response (number and diameter) on day of AI and higher ovulatory response, in term of number of un-ovulated follicles and CLs as well as percentage of cows responded to produce embryos (71.5%) on day of flushing. Also, embryos of cows in P3 showed acceptable survival rate and quality post-vitrification. The same PMSG as a single dose showed the highest response, in term of number of transferable embryos/cow (1.71/cow) and higher survival rate and quality post-vitrification. However, the same PMSG level as 2 doses (1250 IU) at 12-h interval showed the poorest results. Further studies are required to study the problem of decreasing ovulation rate of cows super-ovulated by 4 dose of PMSG (625 IU) by increasing level of GnRH or using LH on day of AI.