الفهرس 
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Abstract
The present study was carried out to evaluate three trials for improvement of in vitro production of cattle embryos.
We conducted our work using slaughterhouse immature bovine oocytes (n=1197), which were submitted to the three experimental trials as follows:
Experiment one:
The aim of this experiment was to elucidate the effect of L-carnitine as antioxidant on the in vitro maturation of immature bovine oocytes obtained from slaughterhouse ovaries of apparently normal genitalia following slaghuter of cows.
A total of 702 immature oocytes were divided into 6 groups where oocytes of group one were vitrified in DMSO 40%, those of group two were vitrified in EG 40%, while oocytes of group three were vitrified in a mixture of DMSO 40% and EG 40%. Immature oocytes of group four were vitrified as in group three, but the vitrification solution was supplemented by 5 mM L-carnitine. In group five, the vitrification mixture was supplemented by 10 mM L-carnitine, while oocytes of group six were vitrified in a vitrification mixture supplemented with 15 mM L-carnitine.
Then, the maturation rate was assessed after in vitro maturation of vitrified-thawed immature oocytes. Thereafter, matured oocytes were submitted to embryo production and the viability rate was compared among different groups.
The results revealed beneficial effects of L-carnitine on both in vitro maturation and developmental competence of vitrified-thawed immature bovine oocytes.
The best maturation results were observed for oocytes vitrified in the mixture containing L-carnitine at medium and high levels (79.00 and 81.25%, respectively). On the other hand, the rate of morula-blastocysts production was significantly increased (P<0.05) in group six, compared to groups one and two (85.71 vs 55.56, respectively). Regarding embryo viability rate, supplementation of the vitrification medium with 10 or 15 mM L-carnitine significantly improved embryo viability (58.18 and 60.25%, respectively), when compared to DMSO (20.00%), or EG (30.00%).
Experiment two:
In this experiment, we tried to determine the beneficial effects of co-incubation of frozen-thawed bovine sperm with relaxin on capacitation in vitro. Furthermore, the influence of co-incubation on embryo production (in vitro fertilization) was also evaluated.
Frozen-thawed bovine sperm were incubated with relaxin at 25, 50 and 100 ng/ml. the resultant acrosome reaction % was evaluated after two hours as well as after four hours.
Although not significant, co-incubation of sperm with relaxin for two hours increased the percentage of acrosome-reacted sperm, in relation to control. The percentage or acrosome-reacted sperm was 40, 43 and 40% for sperm incubated with relaxin at 25, 50 and 100 ng/ml, respectively. But it was 33% for control sperm.
After four hours of co-incubation, there was a gradual increase in the percentage of acrosome-reacted sperm in all groups and still the percentage of acrosomal reaction was higher in relaxin 50 and 100 ng/ml (47 and 49%, respectively), compared to 42 and 39% for relaxin 25 ng/ml and control sperm, but this difference was not significant.
Regarding influence of relaxin supplementation into IVF medium on embryo production, the present results indicate that supplementation of relaxin at 15 ng/ml produced significantly higher percentage of viable embryos (73.33%), when compared to lower rates of inclusion (46.76% for 5 ng/ml relaxin). Interestingly, supplementing the IVF medium with 10 ng/ml relaxin yielded the poorest viability of embryos (20.00%) which is unexplainable.
Experiment three:
This experiment aimed to elucidate the effects of exposing immature bovine oocytes (n=255) obtained from slaughter-house ovaries to low level laser therapy (LLLT) on maturation rates.
Excellent (Grade one) immature bovine oocytes were matured in vitro after being exposed to LLLT for variable time periods. Cumulus oocyte complexes were divided into six groups, the first was control groups which were not exposed to LLLT. The second group oocytes were exposed to LLLT for 2 minutes before incubation. Oocytes of group three were irradiated for 4 minutes, while those of group four were irradiated for 6 minutes using vertical polarization and those of group five were irradiated for the same time period but using horizontal polarization of laser beam. COCs of the last group were irradiated for 10 minutes. All COCs were then incubated for 24 hours in CO2 incubator for in vitro maturation.
The results of this experiment show that LLLT for 4 minutes yielded a beneficial photobiomodulation effect reflected in significantly higher rates of oocyte maturation (80.95%), similar to 6 minute LLLT using vertical polarization of laser beam (90.90%). Meanwhile, exposure of COCs to LLLT for 2 minutes did not differ from control unexposed oocytes. In the same context, exposure of COCs to LLLT for 6 minutes using horizontal polarization did not improve maturation (41.30%). The more intriguing finding was the negative impact of exposure of COCs to LLLT for 10 minutes which led to degeneration and denudation of immature oocytes from surrounding cumulus cells.